Peter Capaldi’s final episode of Doctor Who this Christmas will feature Pearl Mackie as Bill Potts and be called Twice Upon a Time, it was revealed this evening (23 July) during a cast panel at San Diego Comic Con. Viewers will have to wait until Christmas to discover exactly how Bill, who will appear throughout the episode, makes her return.

Join the Doctor, as he teams up with an investigative journalist, and a superhero to save New York from a deadly alien threat.

The Doctor and Clara face their Last Christmas. Trapped on an Arctic base, under attack from terrifying creatures, who are you going to call? Santa Claus!