Okay, we are still trying to figure out what the deal is with John Hurt's "Doctor".
What we know, he did something the Doctor is ashamed of, not being worthy of the title "Doctor".
Here are the four theories I've heard.
The "First" Doctor- He is an incarnation that precedes Hartnell's. before he earned the title.
The "Third Doctor"... We never really saw Troughton's Doctor turn into Pertwee's. So the theory here is that he spent time in this incarnation and was exiled to Earth after being turned into Pertwee's version.
The "Ninth Doctor". We never saw McGann's doctor turn into Eccelston's version. This is the most popular one right now, because his costume seems to be a combination of those two's costumes. It also kind of makes sense because the Doctor did really do something terrible- He wiped out the Time Lords and the Daleks.
The "Last" Doctor- He's the version of the Doctor at the end of his life, the one who falls at Trenzinor.
The "Ninth" Doctor theory seems most plausible, which is why I think it won't be that one, given the producer's history of setting something up and then faking us out at the last minute.