Watch Doctor Who Regenerate As Jodie Whittaker

It's a bittersweet moment for fans of Peter Capaldi but an exciting time for Doctor Who fans.

We finally know who Capaldi's Twelfth Doctor says goodbye and regenerates into Jodie Whittaker as the first female Doctor in the history of the iconic show. We've known this moment was coming ever since Whittaker was announced as the Thirteenth Doctor back in July, and it happened in the Christmas special "Twice Upon a Time."

The official Doctor Who Facebook has video of the regeneration along with the caption: "The time has come. Let the regeneration begin..."

Mark Gatiss, who appears in the episode, told Entertainment Weekly all about the episode. "As we discovered at the climax of the last season, the Doctor is about to regenerate, but doesn't want to. Not because he doesn't want to change his face but [he thinks] maybe this is time to finish it. And then unexpectedly, out of the snow, arrives his very first incarnation, now played by the great David Bradley.... It's essentially a kind of chamber piece of David, and Peter, and Pearl [Mackie], and me, and this strange mysterious threat. But really it's about the wonderful interplay between the two Doctors. Both Doctors are about to regenerate, one of them for the first time, one for the 13th, or whatever it is now. It's a very charming, funny, and rather moving script."

The episode was written by showrunner Steven Moffat, who is also departing the series after eight years. Chris Chibnall (Broadchurch) will take over as Whittaker's era begins.

"I'm beyond excited to begin this epic journey—with Chris and with every Whovian on this planet," Whittaker said at the time of her casting announcement. "It's more than an honor to play the Doctor. It means remembering everyone I used to be while stepping forward to embrace everything the Doctor stands for: hope. I can't wait."