The following post is going to be two things. Firstly it will be a spoiler filled post - I will spoil the ending to the final episode of series seven of Doctor Who (The Name of the Doctor). The second thing it will be is a post full of fan-boy speculation about what comes next. If neither of these appeal to you I suggest you head on to Facebook, or do something slightly more productive with you life... Failing that you can read my thoughts!
To cut a long story short, by the end of the episode Clara has seen out the Doctor's entire time stream, past and future, this includes all his eleven faces. But right at the end we are introduced to another face - another Doctor's face. It is a face the Matt Smith's Doctor does not want to see, he tries to pull Clara away from him, but it is revealed that this Doctor is the Doctor who did not live up to his name. As the episode ends, this Doctor turns to reveal John Hurt.
He is facing the camera for less than 10 seconds, barely says anything, but you can see his is an angry and broken man. His eyes captivate the screen communicating that he has seen a lot with them, made a really difficult decision, and is hardened to what he has done. Matt Smith's Doctor runs from Hurt, almost ashamed of this man, knowing who he is, knowing what he has done. John Hurt's Doctor is a Doctor from Matt Smith's Doctor's past.
My fan-boy theory is that we have been numbering our Doctor's incorrectly. We assumed that when we met Christopher Eccleston's Doctor that he had regenerated straight from Paul McGann, but what would happen if John Hurt's Doctor came between them?
When we first meet Eccleston's Doctor he is fresh from a regeneration, that much is clear. He doesn't recognise his own face, he is looking at himself in the mirror. We later discover that he is an angry Doctor, fresh from the fight of the Last Great Time War between the Time Lords and the Daleks, one which he has just sacrificed both races to end the war. That must have come at a cost to himself too though. What would happen the Doctor who fought in the Time War was John Hurt and he was forced to regenerate at the end of it?
That's my theory, and John Hurt is also wearing a very leathery Ecclestonesque jacket at the end. I think it fits. What I expect the 50th anniversary episode to be is a story about the Last Great Time War, where we see John Hurt's Doctor have to make an impossible decision to destroy his own people.
I'm sure that there will be a lot more to come, many more theories posted online by other fan-boys and girls. And when the show is released I'm sure that Moffatt will throw in plenty of dead ends, plot twists, and other such goodness to keep the viewers on their toes. But right now... I am excited!