"Twice Upon a Time" is a special episode of the British science fiction television series Doctor Who, broadcast on BBC One on 25 December 2017 as the programme's thirteenth Christmas special. The episode was written by Steven Moffat and directed by Rachel Talalay. 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 also stars David Bradley as the First Doctor. Pearl Mackie 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. Mark Gatiss plays a First World War British army captain. The episode is a continuation of "The Doctor Falls", and takes place during the final serial of the First Doctor, The Tenth Planet (1966); footage from The Tenth Planet is used in the special. "Twice Upon a Time" is Capaldi's fourth and final Christmas special as the Twelfth Doctor, and at the time was the last Doctor Who story to be written and produced by Moffat, who served as the show's executive producer and chief writer since taking over from Russell T Davies in 2010. After the special's broadcast, Moffat was succeeded as executive producer and showrunner by Chris Chibnall.