the moment of his death. Refusing to allow the Captain to die, they escape and take the First Doctor's TARDIS to the planet Villengard in the far future. Alone, the Twelfth Doctor meets with the rogue Dalek Rusty, who has taken refuge from other Daleks hunting it. Given access to the Dalek Hivemind, the Doctor learns that the pilot and its ship, known as Testimony, were created on New Earth, designed to extract people from their timelines at the moment of their death, and archive their memories into glass avatars. "Bill" is one such avatar, created from her memories. Seeing no evil to fight, the Doctors agree to return the Captain to his timeline. Upon arrival, the Captain asks the Doctors to keep an eye on his family, introducing himself as Archibald Hamish Lethbridge-Stewart (implying that he is the ancestor of the Doctor's frequent ally and lifelong friend, the Brigadier, and his daughter Kate Stewart). As time resumes, the Doctors watch as soldiers on both sides begin singing "Silent Night". The Twelfth Doctor explains to the First that he deliberately shifted the Captain's timeline forward to the start of the Christmas truce, to ensure his life would be spared. With the Captain saved, the First Doctor informs the Twelfth that he is now prepared to regenerate and says his goodbyes before returning to his TARDIS. He returns to the South Pole for Ben and Polly and finally regenerates into his second incarnation. Now alone with Bill's avatar, the Twelfth Doctor adamantly contends she is not really Bill, but she argues that memories are what defines a person. Bill's avatar restores the Doctor's memories of Clara Oswald before they are joined by Nardole's avatar. The Doctor, however, refuses to give the avatars testimony of his life. They respect his wish to be alone and leave after he embraces them both. The Doctor then returns to the TARDIS and decides to regenerate, but not before relaying some personal advice to his next incarnation. After the newly regenerated Thirteenth Doctor examines her own reflection, the TARDIS suffers multiple system failures due to damage caused by the delayed regeneration. Falling out of the tumbling ship, the Doctor watches in horror as the time rotor and the console room explode, and the TARDIS dematerialises while she plummets towards the Earth below. Continuity "Twice Upon a Time" takes place towards the end of the First Doctor's