Peter Capaldi has announced he will stand down as Doctor Who in December.
He told Jo Whiley's BBC Radio 2 show: "It [the new series of Doctor Who] will be my last. I feel sad. I love Doctor Who."
The actor, who first stepped into the Tardis in 2013, will leave his role as the 12th Doctor in the 2017 Christmas special.
He said: "It's been a huge pleasure to work with a family - I can't praise the people I've worked with highly.
"I've always been someone who did a lot of things. I've never done a job for three years. I feel it's time to move on to different challenges.
"I just thought 'I love this, but I don't know how long I can do it and give it my best'. If I'm not giving it my best, I don't want to do it.
"I can't thank everyone enough. It's been cosmic."
Mr Capaldi, 58, will return in the 10th series of the relaunched show, for a further 12 episodes starting in April.
His final series will also be the last for writer and executive producer Steven Moffat.
Mr Moffat said: "For years before I ever imagined being involved in Doctor Who, or had ever met the man, I wanted to work with Peter Capaldi.
"I could not have imagined that one day we'd be standing on the Tardis together.
"Like Peter, I'm facing up to leaving the best job I'll ever have, but knowing I do so in the company of the best, and kindest and cleverest of men, makes the saddest of endings a little sweeter.
"But hey, it's a long way from over. Peter's amazing, fiery, turbulent Doctor is still fighting the good fight, and his greatest adventures are yet to come. Monsters of the universe, be on your guard - Capaldi's not done with you yet!"