Pearl Mackie was originally not going to be in the Doctor Who 2017 Christmas special

Fans were delighted to find out that Bill Potts would get one more adventure with Peter Capaldi’s Twelfth Doctor after previously seeming to leave the BBC drama forever in series 10 finale The Doctor Falls.

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In Christmas 2017 special Twice Upon a Time, Bill apparently plays a crucial central role –but according to episode writer Steven Moffat that wasn’t always the case, because in early drafts of the Christmas special, she wasn't included in the story at all.

“[Bill’s involvement] came to me later on actually,” Moffat told RadioTimes.com and other journalists on the set of Twice Upon a Time during the final days of filming.

“I was just starting into the script and we had Mark [Gatiss’s] character and we didn't have Bill and I was thinking, 'It's just proof of format again.' You need someone to whom to explain.

"Not to explain it to the Doctor; that's not what the companion does at all. The companion makes it fun.”

Moffat went on to give some examples of this “fun” from the finished episode, in which Mackie’s Bill apparently has some entertaining interactions with David Bradley’s First Doctor...

“The speed with which, to give one thing away, Bill figures out that this daft old brush is the Doctor is humiliating for the current Doctor,” Moffat told us. “He's horrified that she gets it so fast.

“Those scenes and just Bill's perspective on it [were essential]. And I got so in love with and used to writing that voice in the show that I missed her, and I just wanted her to walk in and say, ‘Hey why is that Tardis so much smaller?’”

Mackie herself was certainly happy to get the call, with the actress singing the praises of the episode’s storyline and her mysterious return.

“I'm pretty excited,” the London-born actress said. “They gave me a call and said, 'Do you want to come back?' Yeah!

"There's a little bit of a mystery surrounding it, but it's nice. Bill's back in full Bill mode to a certain extent. You get to see a bit of the whole 'Bill and the Doctor' rapport again, which is very fun.”

https://youtu.be/oGDbeZ0HJBQ

“It's a wonderful Doctor Who story and it's a wonderful Christmas story,” she went on.

“I think it's going to be so joyous for everyone to watch – and it's really funny as well, which is great. You need that on Christmas Day after a few glasses of wine, don't you?

“It plays very well as a sort of standalone, even if you've not seen the full series - or indeed if you've not seen anything else of Doctor Who either. Which is nice! There's jokes in it, there's fun for kids, and there's fun for adults. I think it's going to be great.”

Sounds like the perfect festive treat AND the perfect send-off for Bill. What more could you ask for under your Christmas tree?

Doctor Who returns to BBC1 this Christmas