A Family Affair

"Potoma Lewis very much enjoys the affections of her husband, and her husband's brother, and her father-in-law, and several of his cousins, and has even dabbled around with her dear husband’s elderly aunt on occasion."

— Finnick Odair, The Victors Project

Adultery is considered to be a betrayal on the cheater's behalf, and a major source of drama because of it. And as family is supposed to look out for one another, when the person they cheat with is a relative of the cheated partner it's all the more of a betrayal, and thus all the more dramatic. Usually it's the wife sleeping with her brother-in-law, or husband sleeping with his sister-in-law, though sometimes it's the parent or child. Doing so means they're almost universally considered a Jerkass for betraying their own loved one's trust, and the affair is usually on the bad end of Good Adultery, Bad Adultery. Of course, it's possible for it to be sympathetic if the relative is far nicer than the spouse being cheated on, or the cheaters wanted to be partners in the first place but had to settle for the other relative. Maybe it's just a sign of a Dysfunctional Family.

While it can involve Settle for Sibling and Love Father, Love Son, those tropes are usually for when the partner is dead or they're not in a relationship, if they ended up pursuing it at all. Of course, it's possible that it leads to a Remarried to the Mistress scenario. The cheating partner might find their in-law to be a Replacement Goldfish to whatever spark they had with their spouse. If the relative turns out to be the father of the spouse's child, it's a Family Relationship Switcheroo. Usually doesn't have anything to do with Incest Is Relative unless the partners were already related, although some cultures may consider it semi-incestuous regardless.

Compare Sibling Triangle, where both siblings are knowingly competing for the third one and Two-Timing with the Bestie, where a character's partner cheats on them with a friend of theirs.

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Examples:

Anime & Manga

• Berserk: The Queen of Midland was the king's second wife; feeling neglected by him, she ended up carrying an affair with his brother Count Julius. While the relationship was purely physical, after his death she came to realize she did truly love him.
• In Bokurano, Hatagai cheats on his girlfriend Ichiko with her little sister Chizuru, which turns out to be one of the less despicable things he does.
• Kanon (Chiho Saito): Gen Mikami sleeps with his fiancee Maria's mother. Maria doesn't take it well.
• Mars (1996): Two significant ones:
  • When they were in middle school Sei dated Shiori, until twin brother Rei took an interest in her and decided to pursue her while they were dating. Shiori willingly participates before breaking up with Sei, making their relationship overlap.
  • Rei's mother Shoko was married to Takayuki and had an affair with his now deceased younger brother Akihiko. Both Rei and Sei are actually his biological kids, not Takayuki's.
• Revolutionary Girl Utena: Akio ends up sleeping with his fiancee's mother. He's a lot more of a Manipulative Bastard about it, though.
• Sorcerer Hunters: Throughout the series, the Misu sisters Tira and Chocola are both madly in love with the same man, their fellow Hunter Carrot Glace, mutually deciding that the only woman they will allow to marry him is one of them. In the finale, Tira marries Carrot, but Chocola plans to become Carrot's mistress on the side. She even attempts to sneak into Carrot's bed on the honeymoon so she'll be the first sister to bear his child. Ironically, throughout the series, Carrot barely notices them, and when he does, makes it clear he prefers Tira.

Comic Books

• Batman: Post-Crisis, Commissioner Gordon became Barbara Gordon's uncle and adoptive father rather than her biological father as he had been before, but Barbara later discovered that he may have been sleeping with his brother's wife around the time she was conceived, implying she may have been his biological daughter.
• Spider-Man: Norman Osborn had an affair with his son's fiancée Lily Hollister. This isn't even the worst thing he's done to Harry.
• Wonder Woman:
  • Wonder Woman (1987): While Aphrodite's parentage is left vague, she cheats on her husband Hephaestus with his brother Ares, and has several children with Ares.
  • Wonder Woman (2011): Aphrodite cheats on her husband Hephaestus with his brother Ares, though the children who are normally attributed to Ares and Aphrodite are claimed to be her children with Hephaestus here.

Fan Works

• Brockton's Celestial Forge: Joe unwittingly reveals to Amy the possibility that Carol had an affair with her brother-in-law, and that it may have resulted in Victoria's conception. This information then gets spread around, basically destroying New Wave.
• Downplayed in Chemistry. Cadance is attracted to her husband's younger sister Twilight, but it's likely unrequited.
• Restraint: While Azula was away for two years, Ty Lee cheated on her with her married brother Zuko. This ended up leading to a pregnancy and their Big, Screwed-Up Family became even more screwed up.
• As seen above in the page quote, in The Victors Project, Finnick reveals during "The Revenge of Finnick Odair" that a Capitol citizen cheated on her husband with several of his family members.

Films — Live Action

• The HBO movie Above Suspicion, starring Christopher Reeve and Kim Cattrall as husband and wife Dempsey and Gail, in which Gail is having an affair with Dempsey's brother Nick. Dempsey ends up killing them both and successfully spinning it as self-defense.
• In Bumblebee, Roy, the corrupt hick who explodes into goop by Decepticons Shatter & Dropkick when they first arrive, apparently attempted (and failed) to cheat on his wife with her sister, and cares more about his car than he does the lives of anyone around him.
• Hellraiser:
  • In the original Hellraiser, Frank Cotton is revealed in flashbacks to have seduced his brother Larry's second wife Julia while he was away from home. Her lingering affection for him is the primary reason why she tries to help him complete his resurrection after his escape from the Cenobites.
  • Hellraiser: Judgement: Sean's brother David, who is also his colleague and partner in the police department, is having an affair with Sean's wife Alison. Sean tries to use this sin to offer them as a sacrifice to Pinhead in exchange for his own soul.
• In How to Make an American Quilt, it's eventually revealed that the long-standing issue between sisters Hyacinth and Gladiola is that while Hy's husband was dying in the hospital, Hy slept with Gladdy's husband Arthur.
• Ken Park: The teenager Shawn is sleeping with his girlfriend's mother behind her back and fantasizes about having a three-way with the two of them. Out of the four main characters, whose lives are rife with abuse and dysfunction, his situation is probably the least psychologically messed up.
• In The Killer That Stalked New York, Matt cheats on his wife Sheila with her sister Francie. Sheila finds out about this from Willie, the owner of the nightclub where Matt works.
• Very early in Kiss Me Guido, protagonist Frankie walks in on his fiancee having sex with his brother on the kitchen counter. This betrayal launches the plot, as it drives Frankie to move away and pursue his acting dreams.
• In Love Actually, Jamie's storyline begins with him discovering his girlfriend is having an affair with his brother.
• It's implied in Ophelia (based upon Hamlet) that Gertrude has an affair with her husband's brother, Claudius, or at the very least an emotional affair if not a physical one. She and Claudius are quite flirty with each other while she's still married to Hamlet's father and they even kiss, but Gertrude breaks it off. However, Ophelia later sees her sneaking out of her chambers late at night, possibly to meet Claudius, though it's left ambiguous; after the king's death Hamlet asks Ophelia outright if his mother was unfaithful to his father, but Ophelia can't say for certain.
• A Recipe for Seduction: During a discussion at the bar, it's revealed that Bunny had an affair with Billy, her daughter's boyfriend. One of Bunny's motivations for having Jessica marry him is so she can continue being with him as well.
• The Rental: Mina is in a relationship with Josh, and works with his brother Charlie, who she hooks up with on the first night the group are at the house.
• In Soul Food, Nick cheats on his wife Teri with her cousin Faith.
• Strange Way of Life: Silva accuses Jake of having an affair with his brother's wife. Jake doesn't deny it and simply brushes it off by saying it was a long time ago.

Jokes

• An old joke:
  ''A man goes to meet his fiance's family, and while they all seem friendly enough, he notices that her younger sister seems quite smitten with him, contriving to jiggle her cleavage whenever he looks in her direction, dropping things and bending over to pick them up while next to him, playing footsies under the table at dinner, etc. Finally he ends up alone in a room, when the sister enters half-naked and orders him in no uncertain terms to ravish her then and there, adding that her sister will never know anything about it. Without a word, the man gets up, leaves the room, goes down the stairs, exits the house, and already has his car keys out when the rest of the family pops out of hiding, the father putting down his baseball bat to congratulate him on passing the faithfulness test.
  The moral of the story: Always keep your condoms in the car.''

Literature

• Cloud Atlas: The main reason why Timothy Cavendish is locked up in a home is that he slept with his brother Denholme's wife Georgette. They seemed to have a bad relationship before this, but it certainly didn't help.
• In East of Eden, Catherine cheats on Adam Trask with his brother Charles.
• The Folk of the Air:
  • The heroine Jude Duarte starts a relationship with Locke. She later discovers that he is in a secret relationship with her sister Taryn, whom he even later marries. Locke started his relationship with Jude because he loves to create drama and scandal.
  • Locke's mother Liriope was a consort of High King Eldred, but she also slept with his son Prince Dain. This ends up costing her her life, since Dain murdered her after he found out she was pregnant.
• In Hurog, Ward's father in the backstory had an affair with the half-sister of his wife (Ward's mother).
• Judge Dee: One case involved a young man having an affair with one of his father's young concubines, even planning to murder his father and frame a local artist who claimed the father was a traitor to his country. Unfortunately, in Confucianist China the issue of disrespecting one's father is so important that the son might as well have been screwing his biological mother, and the judge indirectly orders him to commit suicide (the father was murdered, but for entirely different reasons by someone else).
• Modern Faerie Tales: In the novel Valiant, the teenaged heroine Valerie Russel discovers that her boyfriend Tom is sleeping with her mother. This causes her to run away from home due to feeling betrayed.
• A Song of Ice and Fire
  • The justification for the Blackfyre Rebellion's cause is the rumors that the current king, Daeron Targaryen, wasn't actually King Aegon IV's son. Rather, he was the result of Queen Naerys cheating on his, or rather their brother and kingsguard Aemon the Dragonknight. Since Dameon Blackfyre was a legitimized bastard of Aemon and Daena the Defiant, he and his descendants would have more of a claim to the throne if it were true. In-universe most believe this is unlikely due to how pious and honorable Naerys and Aemon were, even if they did love each other, and that Aegon himself started the rumor in order to disinherit his son, especially as the rumours started around the time he was having an argument with his son.
  • After her brother/lover Jaime (with whom she was sleeping throughout her marriage to King Robert) is captured by the Starks, Cersei consoles herself by sleeping with their cousin Lancel, who is apparently closely enough related that he resembles Jaime.
  • "Black" Walder Frey is rumored to have slept with his brothers' and cousins' wives along with his female cousins, and thought to have slept with his great-grandfather Walder Frey's young seventh wife Annara Fanning. This puts the paternity of the younger Freys into question, making House Frey even more of a Big, Screwed-Up Family than it already is.
  • The root cause of Victarion and Euron Greyjoy's feud is that Euron slept with his wife, which Ironborn culture considered her Defiled Forever because of that and Victarion killed his wife out of "honor". While he suspects he raped her, Euron claims she was "wet and willing" and the betrayal is the same. Sadly, this isn't even the worst of what Euron has done to his family or people in general.
• It's implied in Patience and Sarah that Patience's sister-in-law wishes this was happening. Martha gets upset when she learns Patience is in love with a woman, but accidentally lets it slip that she's mad Patience isn't sleeping with someone in the family (AKA, her).
• Mostly Dead Things: Brynn cheated on her husband with his sister, Jessa.
• Ravensong: How Stacey and her siblings were born, as her father of record was effectively infertile, given a trial period of three years:
  Grandpa Thomas told a story of twin brothers, one the father of children, the other the woman's husband. Stacey choked. She isn't going to tell me that Jim is not my father. Momma's monologue softened, became reverent, telling Stacey precisely what she did not want to hear. To prevent divorce and still have children she had spent time in the city with Ned-four times, in fact. It had hurt Jim but he had to decide between no wife and no children or a wife and his twin brother's children.
• The Night's Dawn Trilogy: Dashing space trader/smuggler Joshua Calvert visits a world with the social structures of eighteenth-century England and Louise, a young woman there, develops a crush on him. Her mother, fearing the potential consequences of Louise having pre-marital sex, seduces Calvert in the hope of keeping his penis occupied (it doesn't hurt that her husband is adulterous and that she herself has a crush on Calvert). Calvert seduces Louise anyway, and ultimately ends up marrying her at the end of the series.
• In A Yellow Raft in Blue Water, Ida's father Lecon has an affair with his wife's sister Clara, and to cover this up both Clara and Ida are sent away to a monastery so Clara can give birth and Ida can claim the resulting child, Christine, is actually hers.

Live-Action TV

• This happens a lot in All My Children:
  • Maria cheated on her husband Edmund with his brother Dimitri. She soon after got pregnant, and it wasn't clear who the father was. A Daddy DNA Test revealed Edmund to be the father.
  • Gloria cheated on her fiance Stuart with his twin brother Adam. Stuart broke up with Gloria once he found out, and Gloria and Adam ended up getting married ... with Stuart as the best man.
  • Tad cheated on his girlfriend Liza with her mother Marian.
  • Arlene blackmailed her daughter Hayley's fiance/husband Alec into having an affair with her.
• In the 2000 miniseries Arabian Nights, Sultan Shahryar's distrust of women has its origin in the discovery that his wife was carrying on an affair with his brother.
• Um Anjo Caiu do Céu: One major factor in the Medeiros family becoming a Big, Screwed-Up Family is protagonist João separating from his wife Naná after she discovered him cheating on her with his sister-in-law Laila in a tryst that resulted in him impregnating her with a Heroic Bastard daughter Cuca.
• Doctor Who: Captain Archibald Hamish Lethbridge-Stewart from "Twice Upon a Time" was intended by Steven Moffat to be the Brigadier's grandfather, however according to Henry Lincoln and the Haisman estate (who own the character and publish the spin-off Lethbridge-Stewart series), he was supposed to be his great-uncle, and Alistair Lethbridge-Stewart was the grandfather. A compromise was made with a short story that revealed in a moment of loneliness while Alistair was off on a mission Archibald and Alistair's wife Lillian had a secret tryst, strongly implying that he was the Brigadier's biological grandfather, and Alistair his legal grandfather.
• One episode of CSI: Miami has this as its big reveal. The victims in a double murder are the parents of a teenage girl. The girl's boyfriend killed her father, and the girl arrived in time to see her mother telling the boyfriend that because of what he did, "We can be together now" - he had been sleeping with the mother. Enraged, the girl killed her mother. When the shock wore off, the two teenagers agreed to keep silent.
• On The Get Down, Lydia had quite a bit of sexual tension with her brother-in-law Francisco, who clearly cares more about her and her daughter Mylene than her husband Ramon. It's implied something may have happened between them in the past, which eventually gets confirmed when she reveals to Ramon that Francisco is Mylene's (and possibly her younger daughter's) actual father.
• Helix: Alan became estranged from his brother Peter because the latter was having an affair with Alan's wife Julia, whom he divorced over it. When he's forced into Working with the Ex and learns that Peter's life might be in jeopardy, Alan nevertheless is determined to help his brother.
• The Jerry Springer Show: While cheating in general is pretty common with their guests, this variation also shows up a lot ("You Slept with My Stripper Sister", "He Cheated on Me with My Cousin", etc) as it makes the guests even more likely to start fighting each other.
• Moon Lovers
  • Yeon-hwa implicitly has an affair with 'half-brother Wang Yo, who wants to marry her, but she would much rather marry his full brother Wang So. After Yo's death she eventually makes So marry her.
  • Ha-jin/Hae-su falls in love with Wang Wook, who's married to her distant cousin Myung-hee. After Myung-hee's death Wook offers to marry Ha-jin, but instead she falls in love with his half-brother, the aforementioned Wang So. And in the end she marries yet another half-brother, Wang Jeong.
• On My Name Is Earl, Joy very nearly leaves Earl on their first wedding anniversary for his Manchild cousin that she had hooked up with in the past before meeting Earl. Earl protects her from a killer bee by stabbing it with a skewer from a corn dog, proving to her that he does care about her, and she goes back to him...though she eventually has an affair with Darnell.
• Person of Interest: In Most Likely To... John Reese poses as Frank Mercer to infiltrate a school reunion, and gets slapped by random women. Harold Finches finds out Mercer had a fling with a girl and seduced her mother, who is still sore about it after twenty years.
• Scarlet Heart: Zhang Xiao/Ruo Xi and Yin Si are siblings-in-law but are romantically involved for a while. After breaking up with him Zhang Xiao falls in love with his brother Yin Zhen, and after that relationship ends she marries Yin Ti, yet another brother.

Music

• Voltaire: In "Stuck With You," a husband and wife are both complaining about the other, with increasingly escalating problems. One verse shows that the couple had cheated on each other, starting with the husband:
  Wife: You promised you'd be true to me,
  But gave me infidelity!
  Husband: Why should I give a tinker's cuss?
  She was your sister, what's the fuss?

Myths & Religion

• Classical Mythology:
  • One of the origins of Zagreus and Melinoe is that Zeus slept with his brother Hades's wife Persephone by disguising himself as Hades. Persephone also happened to be Zeus's daughter by his sister Demeter.
  • Ares's favorite consort is Aphrodite, who was married to Hephaestus, blacksmith god and his full brother. While Aphrodite cheated on her Unwanted Spouse with a lot of other people, Ares was the one best known for it.
• The Bible:
  • In the book of Leviticus, several paragraphs are dedicated to admonishing the Israelites not to have sex with family members, including stepparents/stepsiblings/in-laws/etc. Doing so was punishable by the parties involved being burned alive.
  • Later, in the Book of Amos, after Israel has turned (yet again) to idolatry and all-around depravity, the writer laments that a father and son visit the same temple prostitute, or "use the same girl." (Maybe at different times, maybe at the same time; the text doesn't say.) The writer considers this to be a form of incest.
  • Later, in The Four Gospels, John the Baptist calls out a ruler named Herod who is sleeping with his sister-in-law. (He also feels attraction to her daughter, who dances for him at a party.) She ends up having John killed for interfering. (When Herod tells her he'll give her anything she asks for as an award, her mother tells her to ask for John's head on a platter. Herod can't go back on his word, even though he actually kind of liked John apart from the whole "calling him out for having an inappropriate relationship" thing, so he complies.)
  • Later still, in the writings of St. Paul, this is a problem in an early church community Paul is writing to. He gives them a big time What the Hell, Hero?

Theatre

• Chicago: Velma, like all the other "Merry Murderesses" of the Cook County Jail, is a murderer; she killed her own husband and twin sister. In "Cell Block Tango", her motives were explained to have been blind fury at finding her husband and sister having sex after she left for just a few minutes.
• In Hamilton, Angelica remains in love with Alexander even after he marries her sister, and he holds some longing for her as well. This is a reference to the theory some historians believe that the real Hamilton may have had an affair with sister-in-law Angelica.
• Hamlet: After poisoning his brother, King Claudius is quick to comfort the widow and marry Queen Gertrude. It's implied in some adaptations that the two were carrying on an affair while the king was still alive.
• In The Lion in Winter, the French princess Alys has been betrothed to Richard the Lionheart since she was quite young, and has been raised in the English court to prepare her for that role. However, for some time before the start of the play, she's been the mistress of Richard's father, Henry the Second. Henry's wife, Eleanor of Aquitaine, seems to take it fairly in stride and even informs Henry that early in their marriage, she cheated on him - with his father. Henry does not take this in stride, and is in fact physically ill at the idea. (It's hinted that she might be lying just to upset him.)

Video Games

• Metal Gear:
  • Legally Meryl Silverburgh is the son of Roy Campbell's brother Matt, who was killed in the Gulf War. Eventually, it's revealed that he's her real father, as a result of an affair he had with Meryl's mother/his sister-in-law.
  • The wife of Huey Emmerich at one point had an affair with his son (her stepson), Hal. This led Huey to commit suicide and his wife Julie eventually remarried. Her new husband later tried to sexually assault her daughter and was seriously injured in self-defense.
• Summertime Saga: While MC is in a relationship with Eve, he can take Odette up on her offer to have sex with Eve's older sister Grace behind her back. Grace thinks it was a huge mistake, but MC can just continue the affair anyway.
• In The Walking Dead: Season Three, Javier has the option of reciprocating the feelings of his sister-in-law, Kate, whose husband and Javier's brother, David, is presumed dead. Even before the outbreak, Kate and David's relationship was already strained due to him being unpleasant. He's even confided to Javi that he's realized he hates being a family man to the point that he wants to leave and entrust his wife and family to Javi. When it turns out David is alive, it complicates things. He'll be upset when he thinks Javi and Kate are together and accuses Javi of stealing his family (regardless of whether or not Javi has been accepting Kate's advances, Kate deliberately angers David at one point by suddenly kissing Javi). In the ending, Kate won't feel bad if David was killed and urges Javi to do the same, though if Gabe was also killed, she'll ask for some space, but will otherwise want to pursue their relationship.

Visual Novels

• Double Homework has a version of this. Tamara is fully aware that Johanna is attracted to the protagonist, and she actively undermines his relationship with Johanna to get what she wants.

Web Animation

• Harmony & Horror: This is what begins the tragedy surrounding M&H Harmony Toys and the Greywhinder family. Martin's wife Gloria had an affair his brother and fellow co-founder of the toy company Arthur, and as a result those he believed were his children were actually Arthur's and not a miracle as he believed he was sterile. This serves as his Start of Darkness, growing hateful and abusive and eventually making a Deal with the Devil that led to the death of many people, including the ritualistic murder and Fate Worse than Death of his children/biological nephews and nieces. While Arthur had romantic feelings for him, it's ambiguous if her feelings were romantic or she wanted children that carried Martin's "blood".
• Revenge Films:
  • "Brother-in-law’s girlfriend pregnant and she is sleeping with every man in the family": Rose not only slept with both her boyfriend and brother-in-law but also her father-in-law. This is deconstructed, however, as Rose eventually became pregnant and didn't know whose baby it was, causing the three of them to dump her.
  • "My husband was sleeping with my mom, and they disappeared the next day...": Jill's husband cheated on her with her abusive mother. At first, he apologizes to her and begs for forgiveness, but then asks for divorce as he loves the mother more than he does Jill.
  • "My husband was having an affair with my sister": Yuri suspected her husband Jasper was cheating on her. When she caught him going out with her younger sister Zinnia and came over to her mother's house, Zinnia told her the same thing her husband told her when she brought up the affair.
  • "I was called in because my car was caught on a speed camera, but I wasn’t driving it...": Karen cheated on the OP with his own father while he wasn't around, which ended when the bastard died in a car accident after Karen tipped him off. When he found out about it, OP became sick until he collapsed at work because of the accumulated emotional distress.

Webcomics

• Played for Laughs in an early strip of Grrl Power, as Tony and Olivia are half-siblings/cousins^note the technical term is ¾ siblings, as the end result of their father achieving a Twin Threesome Fantasy. Grandma keeps a Laugh Track handy for the inevitable infighting between the twin sisters.

Western Animation

• Family Guy:
  • Attempted but ultimately averted in "Bill and Peter's Bogus Journey". Trying to fix their relationship after cheating on his with Bill Clinton, Lois allows Peter to have an affair of his own so that they're even. He decides to sleep with her mother and she's all for it, but he ultimately can't bring himself to do so. Instead he confronts Bill for being a homewrecker...only to be seduced and bedded by him as well.
  • In "The Munchurian Candidate", Peter performs oral sex on Babs, his mother-in-law, in a hypnotic trance thanks to his Trigger Phrase (the Extra jingle) going off at the worst possible time. When he and Lois find out what happened, they're both too horrified to talk about it until they get back home.

Real Life

• The accusation of this is likely what led to Emperor Constantine condemn and execute his son, Crispus. He was accused of having an affair with the empress and his step-mother Fausta, though it's still debated by historians whether she accused him of the crime or the two actually had an affair. The fact her own children never redeemed her memory when they were in power might support the latter.
• Lady Li of the Northern Liang dynasty had affairs with three of her husband's brothers and attempted to murder one lover's wife.
• Marie Bonaparte (Napoleon's great-grandniece) married Prince George of Greece and Denmark, then had an affair with George's uncle Prince Valdemar of Denmark. Unlike most examples of this trope, George knew about and encouraged their relationship (and he may also have had an affair with his uncle too). At some point Marie also flirted with Valdemar's son, though it's uncertain if that relationship went beyond flirtation. What a mess!

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