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From Lords of the North to Time Lords: "Game of Thrones" star Maisie Williams is to appear in the new series of "Doctor Who".

The BBC has announced Williams joins Peter Capaldi as The Doctor and Jenna Coleman as companion Clara Oswald in the new series, currently filming in the UK. In an as-yet-unspecified "guest role", Williams' character will "challenge the Doctor in very unexpected ways," according to lead writer and Executive Producer Steven Moffatt. "This time [the Doctor] might just be out of his depth, and we know Maisie is going to give him exactly the right sort of hell."

Bristol-born Williams, 17, plays young Arya Stark in HBO's "Game of Thrones". Nominated three times for a Screen Actors Guild Award, she was honoured with the Shooting Stars Award for up-and-coming talent at this year's Berlin Film Festival.

She's also made a name for herself on social media, larking about on Instagram with her on-screen sister Sophie Turner. Turner, who plays Sansa Stark, will also be showing up in a new instalment of a 1960s science fiction institution soon: she's been cast as the young Jean Grey in the next .

The European production and vast cast of "Game of Thrones" means there's a fair bit of crossover between the two hit fantasy shows, especially among the older actors. "Thrones" stars Diana Rigg, Iain Glen, Liam Cunningham, Harry Lloyd, Thomas Brodie-Sangster, Joe Dempsie, David Bradley and Mark Gatiss are just some of the faces who have popped up in the resurrected "Doctor Who" in the last 10 years. Before that, Julian Glover and Donald Sumpter appeared in the classic series of "Doctor Who" before it was revived.

Season 5 of "Game of Thrones" starts chopping off heads, limbs and other body parts on 12 April on HBO, and the following day in the UK on Sky Atlantic and Now TV. "Doctor Who" materialises on BBC One and BBC America this autumn.