He was born of Charles' affair with German socialite Barbara Bloomberg. Due to less than desirable conditions of the topic, Charles kept the child hidden until his death, and it was not until Philip's crowning that the new king found out the pageboy Jerónimo was in reality his own half-brother. As per their father's will, John was accepted into the Spanish Habsburg clan and studied in the University of Alcalá, but he soon turned out to be far from the obedient child Charles had expected. Rejecting his father's wish to become a clergyman, driven instead by dreams of adventure and glory, John pursued the good ol' military life and served some time against Turkish corsairs in the Mediterranean. Moreover, when he received a chance to lead a campaign in the Muslim Rebellion of the Alpujarras, he took it with gusto. He showed talent at defeating the moriscos, but also mercy, because even although his mentor and surrogate father Luis de Quijada was killed in the action, John still took pity on the rebels and interceded in their favor after the revolution was drowned.
His true breakout, however, came then in the 1571 Battle of Lepanto, where Don John, appointed commander of the Catholic fleet and following the advice of the veteran Álvaro de Bazán, led the Christians to a historical and more marketable victory against the Ottoman Empire. To better illustrate John's character, he lifted the spirits of his fleet by dancing a galliard on the deck of his flagship while wearing his full armor, which may sound hysterical to our modern perceptions but actually got the motivational work done. He almost got into a cinematic duel with the enemy admiral Ali Pasha, as the Muslim flagship had managed to ram his own, but the Spanish and Italian boarding parties separated them and allowed the Catholics to capture the enemy ship. Lepanto turned John into the new sensation of the Christian Europe, a young swashbuckling hero soon immortalized in all sorts of memorabilia and whom Pope Pius V literally called a man sent by God. Now, John had a particular ambition aside from cutting people down, which was was to be crowned king of somewhere in order to compensate his shameful origins, and the enterprise seemed wholesome enough that Pius promised him to make him king of the first land he conquered from the Ottomans.
However, it was soon revealed that, for a second time, maybe John was not the Ideal Hero people expected. His next two years in Naples made him known as an unredeemed womanizer, who routinely seduced signorinas of the high society and engaged in displays of economic extravagance that even Bazán was dismayed to witness. John was of the Work Hard, Play Hard type, though, and after considering a proposition to invade the Ottoman-ruled Peloponnese, he proceeded to conquer Tunis, another local asset of the Ottomans in 1573. It seemed like the gold chance had finally come for John to found his own kingdom: he was backed by new Pope Gregorius XIII, had regained a lot of PR by the trivia fact that his own father Charles had also personally conquered Tunis back at its time, and many believed that a Christian kingdom over there would be a great way to keep the Turks away from the western Mediterranean, and hopefully start re-conquering Northern Africa from the clutches of Islam. Then, when it was seemed done, Philip vetoed the project, as he lacked money due to the recently started Dutch Revolt and was uneasy with the idea of giving the rowdy John so much power. Among many discussions, Tunis got lost to the Muslims again, so the thing eventually was All for Nothing for all the Christians involved.
Although discontent with the lost chance, John started anew and became part of an even crazier plan, that of invading England and becoming king with the help of the Pope, Mary of Scotland, and the English Catholics of Richard Stukeley. At the same time, the Dutch Revolt was requiring the crown's attention due to the death of the already ineffective governor, Luis de Requesens (coincidentally a former handler to John), so after another load of discussions, John accepted to replace him on the condition that he would later get assistance for his own English campaign. John seemed to be the perfect Bunny-Ears Lawyer for the occasion, as aside from being an excellent general and a charming negotiator, he had earned lots of money and banking contacts with Lepanto and could finally pay the army that had disastrously mutinied before Requesens' death. Certainly, even although John was bent on solving things quickly in order to focuse on the English enterprise, he seemed to sign a lasting peace with William of Orange by giving out general amnesty, the withdrawal of the army, and several liberties in exhange for submitting again to the king. His invasion of the British Isles had to wait, still, because the plan was not as well-conceived as they believed, and meanwhile the Dutch revolt reopened as soon as the royal armies were out.
The arrival of a good batch of American silver convinced Philip that they were now able to forget about moderation and just crush the rebellion, a visage that satisfied John because that meant they would be free to finally invade England. Reinforced by new troops brought by his close friend Alexander Farnese, John defeated the insurgents in Gembloux, a textbook annihilation that drove several of the rebel provinces to nope out of the rebellion. However, watching the regional tide turn in favor of Spain, a French-English-German coalition was formed by Queen Elizabeth I of England, the Duke of Anjou and the Count Palatine to assist the rebels, and when the increasingly impatient John tried to end it already with a daring surprise attack on them in Rijmenam (which Farnese and the rest of his circle had begged him not to do), he was beaten back. John then asked for a bit more reinforcements... only to find out that Philip had completely changed his mind about his half-brother and was going to recall him back to Spain, as the royal secretary Antonio Pérez del Hierro had supposedly find proof that John was playing a double game in the Netherlands and was planning to treacherously oust Philip himself.
This plot twist was surely false, as it would later turn out that Pérez del Hierro himself was rotten, but by that point John was known for his unconventional ways and his clashes with Philip, which made the thing sound fatidically credible to many. John essentially suffered a Heroic BSoD with the whole situation, fell in a depression, and had time to fall ill and die of an infection in a botched surgery (or poisoned on the evil Philip's orders, the rebels claimed). His last thought was one of service, leaving in his last will that, at least, Philip appointed Farnese the next governor, believing only he could finish the campaign. To avoid John's corpse being captured on its way back to Spain, it was cut in four parts, carried separately in secret and reassembled once again in Madrid, possibly the final insult for the former hero of Europe and the man who wanted to be king.
In fiction
Literature- Juan Latino, the black slave turned poet of the Spanish Golden Age, celebrated John in a work named Austriada Cármine.
- G. K. Chesterton's poem Lepanto focuses on his victory and also celebrates him as "the last knight of Europe"
- The historical novel A Knight of Spain (1913) by Marjorie Bowen depicts the relationship between Don John of Austria and his half-brother, Philip.
- The historical romance, Spanish Lover, by Frank H. Spearman (1930), has Don John as its central character.
- The 1953 film Jeromín is a loose biopic about him, based on a novel by Luis Coloma.
