Planet of the Spiders

Planet of the Spiders was a serial of Doctor Who that aired prior to 1981. The serial depicted the regeneration of the Third Doctor into the Fourth Doctor, and the serial was later novelised as a book of the same name. (PROSE: Fanboys)

Important note
This is a in-universe counterpart of the real world Doctor Who television serial Planet of the Spiders that exists within the Doctor's universe. It was mentioned in Fanboys, a short story written by Paul Magrs based heavily upon his childhood with his brother Mark.

The eleventh season of Doctor Who does also exist within the Doctor's universe, however there is no mention of this serial being part of this season by a valid source, despite their real world connection.