1215

1215 was a significant year in English history because it was the year King John signed the Magna Carta. This event was nearly undone on the 3rd and 4th of March by the Master, who had substituted the real John with Kamelion, a shape-shifting android. The Fifth Doctor, Tegan and Turlough, however, managed to avert the Master's plans, after which the Doctor chose to take Kamelion travelling in the TARDIS with them.

The Doctor was knighted by the "fake" King John, but, as it was done in front of many witnesses who didn't know John was Kamelion, it was a de facto "official" knighthood that prefigured the Tenth Doctor's later honour by Victoria. (DW: The King's Demons)