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Another big name is being added to HBO's Game of Thrones prequel pilot.

Miranda Richardson has joined the ensemble cast in what's described as a series regular role.

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No other details were released about the character. The British actress is best known to genre fans having played Rita Skeeter in the Harry Potter franchise, and also had roles in 1999's Sleepy Hollow and 2002's The Hours.

Richardson joins a sprawling cast toplined by Naomi Watts (King Kong) as "a charismatic socialite hiding a dark secret." Other key cast members include: Naomi Ackie (Lady Macbeth), Denise Gough (Angels In America), Jamie Campbell Bower (The Twilight Saga), Sheila Atim (Harlots), Ivanno Jeremiah (Humans) and more.

Production on the prequel is planned for this summer. The project would not air until at least a year after GoT concludes. If greenlit to series, the project theoretically could be on the air in 2020 or 2021. The prequel's showrunner is Jane Goldman (X-Men: First Class) and based on a concept she developed with author George R.R. Martin. We hear a writers room is already up and running working on additional scripts should HBO decide to order more episodes.

There's no official word yet on where the production will film, though the assumption has been that the production will take advantage of GoT‘s established home base in Belfast, Northern Ireland.

Not a lot is known about the prequel's story, which is officially described as: "Taking place thousands of years before the events of Game of Thrones, the series chronicles the world's descent from the golden Age of Heroes into its darkest hour. And only one thing is for sure: from the horrifying secrets of Westeros's history to the true origin of the white walkers, the mysteries of the East to the Starks of legend… it's not the story we think we know." The show's title is rumored to be The Long Night, but that's not confirmed.

Martin has previously told EW that the prequel will be rather different than the original hit show, which returns in April for its final six epsiodes. "Westeros is a very different place" he said. "There's no King's Landing. There's no Iron Throne. There are no Targaryens — Valyria has hardly begun to rise yet with its dragons and the great empire that it built. We're dealing with a different and older world and hopefully that will be part of the fun of the series."

GoT returns April 14. EW.com will have daily GoT coverage until the end of Game of Thrones, including post-episode recaps and interviews. Follow @jameshibberd for GoT scoop. Bookmark our Game of Thrones content hub.

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