the episode and that he would be played by the former Hollyoaks cast member Jared Garfield. Hartnell, Anneke Wills and Michael Craze appeared as the First Doctor, Polly and Ben respectively through archive footage, as also did Patrick Troughton as the freshly regenerated Second Doctor. Nikki Amuka-Bird voices the "Glass Woman". As with the last change of showrunners, Chibnall wrote the final moments of the episode, so as to allow him to write Whittaker's first lines on the show. This happened in the 2010 special "The End of Time", when Moffat took over for Russell T. Davies in the final moments of the episode, writing Matt Smith's first words as the Eleventh Doctor. The episode includes a cameo appearance by Jenna Coleman as Clara Oswald, as the Doctor's memories of Clara, lost during "Hell Bent", are restored. The scene was the last to be filmed for the episode and while Coleman was willing to come back to film, timing between the filming of this special and her work in Victoria was difficult to arrange. Moffat said "How many times have I killed that girl off and she was right there in my last shot! It's absolutely extraordinary. The unkillable Coleman!" Filming The episode was written by Steven Moffat and directed by Rachel Talalay, who wrote and directed the two-part finale of the tenth series, "World Enough and Time" / "The Doctor Falls", respectively. In January 2016, Moffat announced that he would step down as the programme's showrunner after the tenth series, to be replaced by Chris Chibnall beginning with the eleventh series in 2018, but a 2017 Christmas special was not mentioned in the plans at that time. The change in showrunners almost caused the annual episode to be cancelled, as Moffat planned to leave after the tenth series finale and Chibnall did not want to begin his run with a Christmas special. When he learned of Chibnall's plans, Moffat elected to stay long enough to produce one final episode, as he was concerned that the show would lose the coveted 25 December slot in the future if it missed a year. As a result, he had to rewrite his plans for the tenth series finale to allow Capaldi to appear in one more episode. Near the end of the special, the two Doctors part company and return to their respective TARDISes to undergo regeneration. The First Doctor's regeneration is