Having once before played original Doctor William Hartnell in the 50th anniversary "An Adventure in Time and Space" in 2013, Bradley returned here as the late Hartnell's character, the original Doctor himself.
"I am Bill Potts and I'm back", she told the doubtful Doctor and so good has Mackie been in this role - warm, wry and wonder-filled - that it was tempting to yell at the screen: "Oh Bill I really wish you were".
With "Twice Upon a Time" now behind us, it's going to be a quiet couple of months for Doctor Who fans as they buckle down for the winter and prepare for the long wait ahead. Fans also had kind words for Capaldi's portrayal of the iconic character and his parting words for his successor: "Laugh hard".
What a way to pique the interest from the start, and to make sure warily set-in-their-ways Classic Who fans still felt comfortable watching a show which was about to unveil one of the most talked-about television moments of the year - the arrival of Jodie Whittaker as the 13th incarnation of the Doctor, in place of the departing Peter Capaldi.
"Two Doctors stranded in a forbidding snowscape, refusing to face regeneration".
Whittaker will fully begin her role next year alongside Bradley Walsh, Mandip Gill and Tosin Cole. The casting of Whittaker was unveiled in July.
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. So I feel a bit sad about that, but I understand the argument that you need to open it up.
The interplay between the First and 12th Doctors is one of the highlights of this year's Christmas Special. You don't have to be of a gender of someone to be a role model.
The next season premieres in fall 2018.