'Doctor Who' Season 9 Spoilers: Maisie Williams' Character Teased by Peter Capaldi, Cast, Crew

Maisie Williams, star of HBO's Game of Thrones (which returns in 2016 with season six episodes), is easily the biggest guest star on the upcoming ninth season of BBC's iconic series Doctor Who. Ever since she popped up in the first teaser trailer for season nine, fans (Whovians) have been trying to figure out who she's playing and why her character knows the Doctor so well! In a recent video released by BBC America, series star Peter Capaldi and showrunner Steven Moffat talk about Williams' character and tease spoilers for the upcoming season. Watch more below.

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According to Radio Times, Williams is appearing in season nine's two-part special. The first episode is titled "The Girl Who Died," which will be followed by "The Woman Who Lived." This news most likely has you thinking of even more questions about this character!

"I don't want to give away too much about what she does, but what I would say is she is quite 'cosmic' really," Capaldi says in the new BBC America video. "She's not quite what she seems."

Moffat added: "There's a very unique, interesting young/old quality there that just fitted in beautifully with what we were looking for. But beyond that, you'll have to watch and see."

In regards to working with the actress that portrays Arya Stark for HBO, Capaldi couldn't hold back his excitement!

"She is fantastic. She's such a gifted actress," he said. "The reason I'm saying that with awe is because she's so young. She turned 18 while she was working with us, and she came in and she did a performance that I thought was so mature and so clever."

Watch this new video featuring Capaldi and Moffat right here:

Let us know what you think of this Doctor Who news in the comments section below!