In an interview with VH1 regarding his future career prospects, current Doctor Who star Matt Smith confirmed he won't be sticking with the role past the upcoming 2012/2013 season.
Smith will be heading to Hollywood - a place where handsome British accented men are very welcome - to try his hand at American cinema.
The pertinent line is this. "I’ve got another year of Doctor Who," he said, "but then I’m certainly going to come and give it a shot, come and hang out in LA."
Perhaps he’s just being modest about being asked back, but that’s unlikely. It seems like Smith has already decided that he'll be done with the series after next season. This would place the regeneration of the next Doctor squarely in the 50th anniversary celebratory season of 2013. Smith's successor will be the twelfth actor to play the part.
It’s especially telling if you consider the previous hints he dropped, seemingly accidentally in past interviews. When he was interviewed by The Radio Times this summer, in response to a question about type-casting, he said that he didn’t have any worries about that because "When I finish [Doctor Who], I’ll be…" he paused at this point, seemingly realizing that he was about to give something away, "Well, I don’t know how old I’ll be, but by the end of next year I’ll be 29 so…" then he paused again, seemingly realizing that he’d given something away.
It would not be unprecedented for an actor to only do three seasons as The Doctor, in fact it’s longer than the ninth Doctor, who only completed one season before leaving the show on poor terms.
When Matt Smith began in the role at the beginning of the previous season, he received a mixed reaction from fans, mostly because the previous actor, David Tennant was so well loved by audiences.
Since then, however, he has become one of the most popular Doctors ever - coinciding with the official expansion of the franchise into American television.
Previously, it was shown in the States nearly six months behind the broadcast in Britain. The current season of Doctor Who was the first to be broadcast simultaneously (to the day only) on both sides of the Altantic.
The 2010/2011 season of Doctor Who ended earlier this month, but there is a holiday special planned for the winter. The next season will span 2012 and 2013, but most of the filming will likely take place in 2012. Of course, it’s possible that the doctor could be regenerated mid-season - but this remains highly unlikely.