"Twice Upon a Time" is an episode of the British science fiction television series Doctor Who, written by Steven Moffat, directed by Rachel Talalay, and was broadcast as the thirteenth (and to date final) Christmas special on 25 December 2017 on BBC One. It features the final regular appearance of Peter Capaldi as the Twelfth Doctor, the first official appearance of Jodie Whittaker as the Thirteenth Doctor, and guest-stars David Bradley as the First Doctor, having previously portrayed original First Doctor actor William Hartnell in the 2013 docudrama An Adventure in Space and Time. Pearl Mackie guest stars as the Twelfth Doctor's former companion Bill Potts, while his other companions make guest appearances –Jenna Coleman as Clara Oswald and Matt Lucas as Nardole.