Tennant will remain for four upcoming Doctor Who specials, including the now-traditional Christmas special, which were already scheduled in lieu of a regular season for the show in 2009 (in order to accommodate the sellout performances of Hamlet that Tennant has been enjoying on the London stage).
But after that, at the end of 2009, expect Tennant's Tenth Doctor to regenerate and another actor - the eleventh since the show began in 1963 - to take over the role. It will also coincide with the beginning of Stephen Moffatt's reign as showrunner.
As an aside, I'm starting to understand what it's usually like for a Doctor Who fan to have the departure of a Doctor happening on a semi-regular basis. First it was Christopher Eccleston a few years ago, and now Tennant. But as the Doctor would be the first to note, change is the one universal constant, is it not?
Okay so... anyone wanna guess who'll be the next to pilot the TARDIS?