(SPOILER) Remember that it was a Timewar. This doesn't necessarily mean that John Hurt was an incarnation between the 8th and the 9th. It's possible that John Hurt is the doctor's final regeneration and he really is The Valeyard crossing his own timeline.
It has to be a past Doctor because otherwise how would Matt Smith's Doctor know what he had done?
It's possible that the 8th or 9th Doctor was there when he did whatever horrible thing he did.

It's also possible John Hurt is really 8th Doctor but aged the long way after the movie and all the books/audio dramas. (assuming they didn't depict his death, i haven't actually read any of them).


That's the theory I've heard as well. However, why would they introduce him as the Doctor? Only to keep you guessing? Hm.
From your apparent hate of buildup judging by the Game of thrones thread I cant tell if you're joking or if you don't understand the concept of a double twist