Blackwood, Karen Gillan’s real-life cousin, previously appeared in ‘The Eleventh Hour’ and ‘The Big Bang’.
Doctor Who Spoilers report that the episode, thought to be Episode 8, will also feature Ezekiel Wigglesworth as a young Rory and Maya Glace-Green as a younger version of former EastEnders star Nina Toussaint-White’s character Mels.
The site also reveal that Frances Barber, who is playing a character named Madame Kovarian in Episode 7, will return for the episode.