Doctor Who cast ban GoT spoilers from guest star Maisie Williams

The cast of Doctor Who revealed they only had one request when Maisie Williams joined them on set: she wasn't allowed to divulge any Game of Thrones spoilers.

Maisie is set to guest star in one of the upcoming episodes in the ninth series of the show.

Speaking ahead of Comic-Con in San Diego, Doctor Who star Peter Capaldi revealed: "We had to make sure she didn’t give us any GOT spoilers, we didn’t want to know anything at all."

The Doctor Who cast reveal details of Maisie Williams’ guest appearance (PA)

Talking about the character she'll play on Doctor Who, Jenna Coleman (who plays Clara), said: "I don't think we're allowed to give anything away, other than to say she is utterly brilliant as you would expect, and it's a very surprising and intriguing storyline with her connection to us and her connection to the Doctor."

Peter wasn't giving much away, only to say her role was 'cosmic'.

"I love cosmic, it’s such a great word, it covers so many bases,” he said, "She’s wonderful in it, and also, what’s great about Maisie, she changes, she metamorphosizes. She's metamorphic. She’s so different, Without giving anything away, the way she acts, the different aspects of her character, is very exciting and compelling and very impressive for someone who is so young."

Maisie Williams attending the Glamour Women of the Year Awards 2015

Maisie said she was excited by Doctor Who as such an “important part of British culture”

Jenna went on to say: "Immediately from day one it was great to have her around on set, the dynamic worked very well."

When asked which other stars the cast would like to see make guest appearances, Michelle Gomez (who plays Missy, aka The Master), volunteered the Queen and singer Tom Jones.

Jenna said she'd love to have Helena Bonham-Carter star in the show, and Javier Bardem because "he'd be a good villain".