"Game of Thrones" is hoarding accomplished, veteran British actors for its sixth season.

The HBO drama has cast Richard E. Grant in a mystery role for its upcoming season. Grant boasts an impressive resume of film and television work, including recent appearances in "Downton Abbey," "Doctor Who," and "Girls." He also acted in "The Iron Lady," "Gosford Park," and "Withail & I."

There are no details on who Grant is playing. Danish actor Pilou Asbæk is reportedly playing Euron Greyjoy, Theon's uncle. "Unreal" star Freddie Stroma has been cast as Dickon Tarly, Sam's brother. And Max von Sydow will take over the role of the Three-Eyed Raven, who is training Bran Stark in the ways of the warg.

"Game of Thrones" fans are speculating that Grant could be Sam's father, Randyll Tarly, or perhaps the leader of a theatre troupe that mentors Arya Stark. Or Grant could be a character unseen or unheard of before, since the show has outpaced George R. R. Martin's books.

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