Rewatching the new Doctor Who and have a theory.

Both the 9th Doctor and 10th Doctor have said things that were wrong in the Universe they were in, calling Micky "Ricky" and saying that Harriet Jones would be called the Golden Age but then having to dispose of her for using a weapon to kill aliens who were retreating. The Universe they go to in season 2 ending had Ricky and later had Harriets Golden age. I think at the end of the Time War when the Doctor blew up everything and killed off everyone he got blown into that Universe without knowing it. He should be in the other Universe.