EXCLUSIVE: HBO has set Josh Whitehouse to a lead role in HBO’s Game of Thrones prequel pilot from writer Jane Goldman and author/GOT co-executive producer George R.R. Martin that has Naomi Watts heading a fast-forming ensemble cast.

Whitehouse is a British actor who starred in Northern Soul and most recently wrapped the lead role in The Happy Worker, the David Lynch-exec produced drama directed by Lynch protege Duwayne Dunham. Whitehouse next stars in MGM’s musical retelling of the cult classic Valley Girl, playing the lead role originated by Nicolas Cage. He currently can be seen in the BBC series Poldark, and on billboards as the face of Burberry’s new fragrance campaign, ‘Mr. Burberry.’

The story line and roles are being kept close to the vest at HBO, which would not comment.

The untitled prequel takes place thousands of years before the events of Game Of Thrones. It 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.

Watts was announced yesterday to play a charismatic socialite hiding a dark secret.

Goldman serves as showrunner and will executive produce alongside Martin as well as fellow GOT co-executive producer Vince Gerardis and Damages and Bloodline co-creator Daniel Zelman. Added since the June pilot green light are former BBC Studios executive James Farrell and Jim Danger Gray as executive producers and Chris Symes as co-executive producer. As previously announced, GOT creators/exec producers David Benioff and D. B. Weiss have no involvement in the potential offshoots.

Whitehouse is represented by CAA, United Agents in London, Untitled Entertainment, and Gang, Tyre, Ramer & Brown.