Steven Moffat Says One Character Wasn't Originally Supposed to Be in the 'Doctor Who' Christmas Special

Doctor Who's latest Christmas special gave fans quite a lot to take in, from the Thirteenth Doctor's arrival to the surprising return of some old favorites. But as it turns out, one of the episode's standout storylines almost didn't happen.

In a recent interview on Doctor Who: The Fan Show, outgoing showrunner Steven Moffat revealed that Bill Potts' (Pearl Mackie) role in "Twice Upon a Time" was actually added into the script later on. As Moffat revealed, the idea initially came from the nature of the unique relationship between the Twelfth Doctor (Peter Capaldi) and the First Doctor (David Bradley).

"I was 20 pages into the script and I was slightly stuck." Moffat explained. "And I thought: 'I just want to hear what Bill's got to say.' I had been so used to writing Bill, and she'd been such an invigorating, exciting presence throughout series 10, I just thought I feel it is wasted, the Doctor meeting his older/younger self, and all his political incorrectness. It is wasted, if Bill does not witness this and comment on this. And if she doesn't instantly work out who that is to the Doctor's horror, if Bill doesn't explain certain aspects of her modern life to the First Doctor, it is wasted."

Ultimately, Bill ended up being one of many companions to make a return, with Clara Oswald (Jenna Coleman) and Nardole (Matt Lucas) briefly appearing. And overall, that reunion with former companions helped contribute to the grand scale of "Twice Upon a Time" - something that Moffat hadn't initially planned for.

"Well, the grand finale to my time on Doctor Who was "The Doctor Falls," and that was the Doctor stating his case and choosing a hill to die on." Moffat told ComicBook.com earlier this week. "That was our grand finale. But we had the awkward business that Chris [Chibnall] didn't want to start with the Christmas episode, quite rightly. So, there was the momentary possibility there wouldn't be any Christmas episode, so I suggested that I do the Christmas episode and talked Peter [Capaldi] into doing one more so that Doctor Who wouldn't lose the slot."

"Having done that, of course, we had the problem of doing the grand finale plus an hour." Moffat continued. "And so it's a different kind of story. It's a story about the Twelfth Doctor, the Doctor himself at the end of his life, thinking, "I don't know if I can keep doing this, I'm tired," and finding the strength to carry on. You see, it's a Christmas story resurrection for both him and for the First Doctor who's in the same mental state. So they both have to convince each other that one more regeneration is possible. So it's that kind of story."

Doctor Who will return in the fall of 2018.