By the old gods and the new, this has been a busy week for the Game of Thrones prequel: Josh Whitehouse has joined the pilot, our sister site Deadline reports, following Naomi Watts’ casting which was announced Tuesday.

The Poldark actor will play a lead role in the spinoff, though no other details currently are available. As previously reported, Watts will play a “charismatic socialite hiding a dark secret.”

HBO formally ordered a pilot for the Game of Thrones prequel over the summer, with the action taking place thousands of years before the events of Game of Thrones. According to the official logline, “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’ 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.”

Jane Goldman (X-Men: First Class) wrote the pilot and will executive-produce alongside author/GOTco-EP George R.R. Martin. “We are doing a pilot that Jane Goldman wrote,” HBO programming president Casey Bloys confirmed for reporters at the Television Critics Association in July. With HBO exploring five different GoT spinoff concepts, “we’d be lucky to get one that we’re very, very excited about, and we did get that.”