Game of Thrones' star Maisie Williams has hinted that her Doctor Who character could be a "goodie" or a "baddie".

The Game of Thrones actress is to guest star in the sci-fi drama when it returns for its ninth run in the autumn.

Speaking to Alan Carr on his Channel 4 Chatty Man show, which will be broadcast tonight (Friday April 10),Williams also spoke about testing Peter Capaldi's Doctor and his Companion Clara Oswald, played by Jenna Coleman.

"There's been a lot of speculation about whether she's like a younger Clara or whether she is a new character completely," she said. "I'm not going to tell you which one.

"Whether she is good or bad is up for discussion, I think. She does put the Doctor to the test and it's sort of a dynamic that we haven't seen before."

On joining the hugely popular BBC sci-fi series, she added: "It's wonderful. The set's amazing.

"I'm used to being part of Game of Thrones and going into something where you're a small part of something else. You don't want to hold anything up because they've got such a well-oiled machine going.

"Everyone is so accommodating and lovely and happy to have me. There's no rivalry that I thought there would be – 'You're from Game of Thrones' and I'm like, 'You're from Doctor Who'. They're really lovely."