'Downton Abbey' actor Richard E. Grant has been officially cast in 'Game of Thrones' season 6

The very talented actor Richard E. Grant will be joining the cast of "Game of Thrones" for Season 6, an HBO representative told Business Insider.

First reported by "GOT" fan site Watchers on the Wall, Grant's role has yet to be revealed.

According to the fan site, there are several unfilled roles that could fit the actor. They include Randyll Tarly, Aeron Greyjoy, and Lord Karstark.

Grant has a robust acting resume with television credits dating back more than three decades, including PBS's "Downton Abbey," HBO's "Girls," BBC's "Doctor Who," and USA Network's "DIG."

He will join a few other confirmed newcomers for Season 6, including Pilou Asbåk as Euron Greyjoy, Ian McShane in an unspecified role, and Max von Sydow, who will take over the role of Bran Stark's (Isaac Hempstead Wright) mentor, the mysterious Three-Eyed Raven.

"Game of Thrones" returns to HBO in spring 2016.