2. The Eight-Nine Bridge?
This ties in with the theory that Hurt plays the Doctor which existed during the destructive Time War. Discounting all the radio plays and books which have appeared since, the Eighth Doctor only appears in the one-off 1996 TV movie, and we don't see him regenerate into the Ninth Doctor, who appeared out of nowhere in the episode Rose and helmed the series in 2005. Yet, even though Russell T. Davies confirmed there was no regeneration sequence for the sake of practicality and for a fresh start for new watchers, it raises the question as to exactly why viewers were not treated to some sort of regeneration, or explanation, as to why Paul McGann regenerated into Chris Eccleston. Maybe it was because, as mentioned before, the Doctor regenerated again and hid the incarnation which was present during the Time War as a result of shame or, perhaps, necessity. For starters, in Rose, the Ninth Doctor expresses surprise when looking in the mirror, so we can presume that he regenerated a short period previously (or hasn't been in the company of many mirrors). Either way, the regeneration has occurred, but again, Eccleston's Doctor was an edgy, gritty, hardened character, who when facing the Daleks showed hatred and contempt (then again, so does every incarnation). What we might be able to presume then, is that McGann regenerated into Hurt, who can be presumed to then fight in the Time War and cause something to occur which wiped out the Daleks and the Time Lords (who were seen as a power-hungry defeated race in The End of Time). The Doctor's words of shame and sadness in the revived series appear to indicate his involvement in such an event, so it appears that he regenerated again, and hid the incarnation away. But this can only be theory until the 50th anniversary is broadcast later this year.