VIDEOS:
Farewell, K9. Hello, K9 Mk II.
After wrapping up the plot, the Doctor prepares to go back to the TARDIS with Leela and K9, only to find out that they've both chosen to stay on Gallifrey. The Doctor solemnly bids them farewell and heads off in the TARDIS on his own, then immediately fishes out a box labeled "K9 MII" before giving a cheeky smile to the camera.
Example of:
Replacement Goldfish