David Tennant has been filming some of his first scenes as the new Doctor Who - and Newsround was there to watch the events unfold behind the scenes.
David becomes the 10th Doctor. He takes over from Christopher Eccleston, who helped revive the show and make it a massive success.
The actor said he was nervous and excited about taking on the job.
"It's great to get to play a TimeLord and have a Tardis," he said, adding that he was also a bit scared.
Doctor Who has been attracting up to 10m viewers. The programme-makers are keeping the same formula, but with a new face in the main role.
"If it all goes wrong, it's my fault. I'm the only new guy" joked David. "It just adds to the scariness factor."
Viewers will be able to find out how David gets on when his scenes hit the screen at Christmas.
Billie Piper remains the Doctor's companion, Rose Tyler, travelling through time and space battling aliens.
She said he was "absolutely perfect" as the Doctor.