The actress will return one last time for the new episode.
This Christmas, the Doctor will be regenerating all over again, with Jodie Whittaker taking over the titular role in 'Doctor Who' and becoming the first female-bodied version of the character to ever hit the small screen. It's a historic moment, but not one we'll see before Peter Capaldi has one last adventure as the iconic sci-fi star.
Pearl Mackie at San Diego Comic-Con earlier this year
Joined by David Bradley, who's taking on the role of the First Doctor (originally played by William Hartnell) along with his companion Bill (Pearl Mackie), the three will be enjoying their final episode of the franchise before Whittaker and a new companion in the widely rumoured form of Bradley Walsh make their proper debut next year.
So, will this year's 'Doctor Who' follow in the vein of 'EastEnders' and deliver all doom and gloom, or will the uplifting fun of the 'Doctor Who' Christmas specials in the past have an impact on what we'll digest? It would seem like the latter, as Mackie has been chatting about her upcoming final episode.
Speaking on Sunday Brunch this weekend (December 17), the actress teased: "There's two Doctors - well three Doctors in it, technically, isn't there? You've got Peter as the Twelfth Doctor who is struggling with not wanting to regenerate and he meets the First Doctor, played by David Bradley, who is absolutely amazing.
"The dynamic they have between the two of them is so funny [...] It's amazing. Their dynamic together is absolutely hilarious."
We've seen a little of Capaldi and Bradley together in the last series' finale, but this will be the first time they really get to play off of one another, and we couldn't be more excited to watch it all down.
"It's a lovely episode [...] and it's Christmassy," concludes Mackie. "And there are two TARDISes, and I'm in it! It's very exciting." We can't wait.
See the 'Doctor Who' Christmas special on Christmas Day (December 25), on BBC One at 5.30pm.