This Friday, as part of the BBC’s Children In Need telethon, we’re getting the now-traditional preview of the Doctor Who Christmas special. Twice Upon A Time will, of course, star Peter Capaldi and David Bradley as different iterations of the Doctor, with Jodie Whittaker appearing at the end of the episode too.

Twice Upon A Time will be Steven Moffat’s last script as Who showrunner, and he’s teased the episode a little in the extra features on the Doctor Who series 10 disc release. The discs went on sale at the start of the week, and Moffat has said that “David Bradley is such a good swap for William Hartnell. He looks so like him and can so capture that part”.

But intriguingly, Moffat teased that “we could actually have in effect William Hartnell returning to Doctor Who, and witness to his great horror what he has become”.

This ties into previous teases Moffat has offered about the episode, that suggests that Bradley’s take on the Doctor won’t be best pleased with how he’s turned out many regenerations down the line.

Twice Upon A Time screens on Christmas Day on BBC One. The exact transmission time has yet to be confirmed.