Tennant contemplates 'Doctor Who' exit

David Tennant has a firm idea of when he will leave Doctor Who, but refused to comment on any exact date.

"I think I now know how many series I'm going to do," he reveals in this month's Doctor Who Magazine. "I think it would be stupid of me to say more than that right now, before this series has even begun filming. Anything can happen, and everything can change."

Tennant also described his sadness at the absence of former sidekick Billie Piper: "Billie was the only other cast member there every single day, and we relied on each other professionally, and personally, and I do miss her a lot."

However, the Scot leapt to the defence of new co-star Freema Agyeman, who will portray Martha Jones in the third season of the revived sci-fi show. "She's no reason to be daunted or nervous, because she can palpably do it - she's obviously a good actress. This show gets a lot of scrutiny, so she wouldn't have got the gig unless everyone was certain she could do it," Tennant said, before adding: "It'll be fascinating to see how she slots into the team."