David Tennant has announced he will leave Doctor Who after filming a string of special episodes next year.
Here he explains why he's leaving...
So why have you decided to say goodbye to Doctor Who?
When I first started back in 2005, I always thought that if it worked out, three years would be about the right time.
Three years, three series. Which I did and I loved and I had a great time. And with Russell T Davies and Julie Gardner [executive producers] leaving, that became a very natural stepping off point for me.
What became very difficult was when it was announced that Steven Moffatt was taking over because I'm such a fan of his, he's such a great writer, he's written such amazing stories for me in Doctor Who already.
The prospect of hanging around for a while and enjoying working with him was sorely tempting and very nearly changed my mind.
But I think it's better to go when there's a chance that people might miss you, rather than to hang around and outstay your welcome.
What's your message to the fans?
When I was a kid, I loved Doctor Who, I grew up with it. For me, it was the most exciting time when the Doctor changed.
You know he's on his way out, you know something terrible's going to happen, it's very exciting - and then you've got this whole new character to look forward and wonder about.
It's very exciting and it's part of what makes Doctor Who so great. I'm excited as a viewer to see what happens next.
Russell T Davies must have given you some hints about what your exit will be like?
No! He hasn't. I do not know what he's thinking about. But Russell being Russell, I'm sure it'll be a send off to be proud of.
What are your memories of the last three-and-a-bit years?
It's been the most extraordinary time, it's been bewildering, life changing, very exciting. And just so much fun, such a great show to work on.
And again I think that's one of the reasons I think it's right to take a deep breath and bow out when it's still fun, when it's a novelty.
I don't ever want it to feel like a job, so I want to move on when it still feels exciting and fresh and that means I'll miss it.
What do you think you'll miss the most?
I think I'll miss all the people who work on the show. I'll miss Russell's fantastic scripts and of all the other writers who work on it.
And I'll miss playing this character. I don't think there's a better character on television.
He gets to be everything - he gets to be funny and intense, he's a hero but he's also a bit of a clown, he's an anarchist but he's strong and dependable and crazy.
Like mercury one minute and like steel the next.
And to get the chance to play all those things for 45 minutes on a Saturday night - I'll miss that I'm sure.
As an actor, do you think you'll always be known as Doctor Who?
I think it's one of those parts that does that does follow you around, yeah.
I know a couple of the old Doctors and it's clearly still a part of their life.
I think the public has such an enthusiasm for it and such an intrigue for the show, that once you've been part of it it does tend to stick to you like glue.
But that's fine - it's something I'm very proud to be forever associated with.
Do you think you'll ever do anything as special as Doctor Who again?
It's difficult to know… I can't think of anything else that has fans who are seven and 70 in almost equal measure.
It's difficult to think of what else one might do that could rival that.
I hope I'll do things that will be as exciting and as thrilling artistically and professionally, obviously, but I think Doctor Who is pretty unique.
Whoever your successor turns out to be, what would your advice be to them?
I wouldn't be as pompous as to offer them advice - I'm sure they'll sort it out for themselves.
Just have fun. It's the best part around. Enjoy it.
What will it be like for the fans - you're their Doctor and it will be a huge change for them when you go?
I guess if you were eight when I took over, you'll be 12 when I leave, which is quite a big time of life isn't it?
But I think that's one of the exciting parts of being a fan of the show - you know that the doctor can change, the character and the centre of the drama can be a completely different person, and act very different.
It's not like James Bond, where you know he's a certain type of man, like Tarzan is a certain type of character, or Sherlock Holmes.
The Doctor can change quite radically, but there's still an essential Doctor-ness and I'm sure whoever takes over will find their own way of communicating that.
And when I was a kid, Tom Baker turned into Peter Davison, and it was thrilling and extraordinary and a little bit disorientating at first, but in a really exciting way, so I'm excited for everyone else getting to watch that happen. I think it'll be great.
You're not leaving immediately - you've got another year for the specials. Can you tell us about that?
We've already shot the Christmas special for this year called The Next Doctor, which in the circumstances is perhaps a more intriguing title than it was before.
We see the 10th Doctor meeting another Doctor.
And then in January we'll film four more specials, which will be screened throughout next year, and they'll be the four last stories that I do.
I don't quite know when they'll go out, but they'll go out sometime throughout 2009.