Jodie Whittaker, who starred in 24 episodes of Broadchurch, will take over for Capaldi at the tale end of the episode when The Doctor regenerates.
Capaldi's portrayal of the iconic time travelling alien from Gallifrey was met with universal critical acclaim. Many latched on to the Thirteenth Doctor's first words, "Oh, brilliant!"
Capaldi's tenure coincided with an overall darker era; he filmed, an appropriately numbered, twelve 12-rated episodes. Comedy Mrs Brown's Boys was the top show on Christmas Day with an average audience of 6.8M, followed by Strictly Come Dancing's Christmas special, Call the Midwife, Eastenders, The Queen's Christmas Broadcast and Doctor Who.
"It's more than an honour to play the Doctor".
And it isn't just Capaldi who was taking his final bow either, as Pearl Mackie's appearance as Bill was her last, though her Testimony role means there's every chance we may see her again in the future.More news: Bitcoin prices on downward spiral in Korea
However, pre-2005, only one of the incarnations actually spoke immediately post-regeneration (in this case, Colin Baker's Sixth Doctor in 1984).
Historically, the Christmas Special itself was actually non-existent until Russell T Davies rebooted the show, introducing Doctor Who to a whole new generation in the Noughties.
With showrunner Steven Moffat departing, Doctor Who will be in the hands of Chris Chibnall going forward, whom Whittaker worked with on Broadchurch.
She's only got one line in the Christmas episode, which was titled Twice Upon a Time, but the appearance certainly made an impact.