Doctor Who is keeping it in the family after show bosses announced Michael Troughton, the son of Patrick who played the second ever Doctor, will appear in the Christmas special.
The actor, whose father replaced William Hartnell in 1966, will join other guest stars including Natalie Gumede and Nick Frost in the festive episode.
Frost, who found fame in Spaced before going on to star in Shaun of the Dead and Hot Fuzz, said: " I'm so thrilled to have been asked to guest in the Doctor Who Christmas special, I'm such a fan of the show. The read-through was very difficult for me; I wanted to keep stuffing my fingers into my ears and scream 'No spoilers!' Every day on set I've had to silence my internal fan boy squeals!"
Show boss Steven Moffat said: " Frost at Christmas - it just makes sense! I worked with Nick on the Tintin movie many years ago and it's a real pleasure to lure him back to television for a ride on the TARDIS."
The new series, the first with Peter Capaldi as the timelord, continues this Saturday with a guest appearance by Line of Duty star Keeley Hawes.