Fans at Comic-Con International in San Diego bid farewell to showrunner Steven Moffat today, as well as Twelfth Doctor Peter Capaldi, companion Pearl Mackie and Master Michelle Gomez. Mark Gatiss also joined the panel, which was hosted in Hall H as part of BBC America's presentation.

Moderator Chris Hardwick opened up the panel by showing the first footage from the upcoming Christmas Special. The episode is called “Twice Upon a Time” and features Pearl Mackie, Bill Potts and David Bradley. Bradley is reprising his role as the First Doctor, William Hartnell. The episode will deal with the Doctor's reluctance to regenerate and will introduce the newly announced Thirteenth Doctor Jodie Whittaker.

After the footage, Hardwick introduced the panelists and then asked Capaldi what he thought of his time on Doctor Who. Capaldi said, that it was, “Fantastic. Time ran away with me. It's been fabulous to work with these guys, to realize that the show is so popular and is so beloved around the world. Thank you for all of your affections."

Hardwick then asked Moffat about the Christmas Special. Moffat said that the “Twelfth Doctor is refusing to regenerate because he wants to stay Scottish, (audience laugh) and the First Doctor is also refusing to regenerate. 12 is saying, 'you have to or all of this all won't happen.' The First Doctor and 12 then go on a crazy adventure with Mark Gatiss and Bill Potts.”

Hardwick then asked Moffat how long ago he started crafting the idea that Bradley would reprise his role as William Hartnell. Moffat said, “It happened at New York Comic Con. He recreated Hartnell with a twinkle, with such grace, he captured what the First Doctor was really like.” Bradley previously played Hartnell in the Gatiss-written docudrama The Adventures of Time and Space during the 50th Anniversary celebrations in 2013.

Hardwick then transitioned to Mackie and asked her about her experience being part of the Doctor Who fandom for the last year. “The response was large,” Mackie said, “but by no means compared to the people sitting in front of you. I don't think I was prepared for how powerful the Doctor Who fandom is. Thanks for having me.” He then asked if Mackie would come back next season. “No. That's it. The Christmas Special is the last chance to see Bill.” She did add, “But it's Doctor Who, never say never.”

Hardwick also asked Mackie what she enjoyed about playing Bill. “Bill was so real. She's inquisitive and quick-witted. She has a childlike curiosity which I think is great because who wants to grow up? She's very strong minded and she believes in everything that she does.”

Hardwick then turned to Lucas, who is also concluding his turn on Doctor Who. “Nardole is a triumph,” Lucas said, “Earth is one of my favorite planets (chuckle).” Lucas also said that, “Growing up I was a fan and when I was 13 they stopped making it. It's a pinch yourself moment when you get asked to be in the show. The Christmas Specials have a slightly different identity than the regular series because they are lighter. I thought I was doing a cameo, what a treat. Across the series, I knew I had to find some nuance and character.”

Hardwick also asked Gomez about her time as the Master. "For Missy, the pull to darkness was too much fun. She could have been two-dimensional, black and white, but to possibly try on good and see how that feels was fun. Capaldi presented me with a challenge, it was hard to act with this man and not want to be your best self.

There was a great friendship once there, between the Master and the Doctor."

Capaldi then weighed in on the announcement of the new Doctor. "Jodie is so full of excitement. It's thrilling to know it's in the hands of someone who cares for it so deeply. She's a great choice. Which led to Moffat interjecting, "Can I just say something as well? There have been all these articles about backlash, there is no backlash. There is 80% approval on social media and yet so many people wanting to make something up that's not there."

Hall H then erupted into a standing ovation for Capaldi, which was a profound moment to witness. Capaldi then launched into praise and thanksgiving for each person on the panel with him. He began by telling Moffat, "Every shot there [Capaldi's tenure video] came through this man's eyes, mind, and generosity. He's an incredibly gifted artist. The message of kindness comes from his heart. The creation of a female doctor comes from a female master, so we owe a female Doctor to Steven Moffat."

Capaldi then continued with Mackie. "Bill has her feet on the ground and heart in the stars, which is where we all want to be. Matt [Lucas] has come along and delivered a fabulous creation – a huge contribution to the show with a generosity of spirit. Mark [Gatiss] is a great lover and supporter of Doctor Who. Mark has written the most fabulous episodes and I'm so thrilled I was able to act with him in the Christmas Special."

The panel concluded with a few questions from fans. One question was aimed at Moffat, about if he is leaving Doctor Who with anything left undone? Moffat answered, "I've written 42 episodes. I've done as much as I can think of. I think what got me through the end was having a finish line. It's time for someone to come in and have much better ideas than me. That's the way it works. It's emotional to leave, but the main thing I'll miss is this."

The final fan asked Capaldi what the hardest thing he had ever done on the show? Capaldi's reply? – "Leaving it."

Capaldi, Mackie, and Moffat's final episode of Doctor Who will air Christmas Day.