David Tennant has announced he will leave the hit UK sci-fi show Doctor Who, after he completes shooting on 4 special episodes scheduled for screening in 2009/2010.

Tennant is the Tenth incarnation of the Time Lord, taking over the role in 1996 from Christopher Eccleston who starred as the Ninth Doctor in the revived BBC series.

Tennant is currently taking a break from the show to pursue his stage theatre career, but has already filmed this year's Christmas special "The Next Doctor", which co-stairs David Morrissey as a man who also claims to be the Doctor.

A 2-minute teaser clip from the 2008 Christmas episode, which features the return of the Cybermen, will screen during the BBC's Children in Need telethon event on Friday November 14th.

Speculation now turns to who might play the Doctor's 11th incarnation when he regenerates in 2010. The BBC has already commissioned a 5th series (or 31rd series, for fans counting since the show's inception in 1963), with veteran writer Stephen Moffett taking over from Russell T Davies as Executive Producer and Head Writer.