Doctor Who is ready to let viewers in on the big secret surrounding Maisie Williams' character.

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Well, not the entire secret. Nevertheless, showrunner Steven Moffat has dished out a healthy dose of spoilers regarding the Game of Thrones star's turn in the TARDIS.

Set to appear in episodes 5 and 6 ("The Girl Who Died," "The Woman Who Lived"), Williams' unnamed character will appear as the Doctor (Peter Capaldi) and Clara (Jenna Coleman) dive into world of the Vikings.

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"It's a significant role, we're not just throwing her away. It's a great part and she's terrific in it," Moffat told the BBC. "One thing I think is worth saying, because it keeps coming up as an issue, is that she is not playing a returning character. She's a new character, she's not a character from the Doctor's past."

So not a younger version of Clara, then.

Photos have shown the 17-year-old as a highway bandit, but it is unknown if the youngster will jump into the role of hero or villain.

"Whether [my character] is good or bad is up for discussion, I think," Williams' teased, according to Chatty Man (via Digital Spy) "She does put the Doctor to the test and it's sort of a dynamic that we haven't seen before."

Find out the truth when Doctor Who returns to the BBC and BBC America this September.