Film production for the untitled show has begun in Northern Ireland, according to the Belfast Telegraph. The local media outlet reports that shooting sites across the province of Belfast were being set up last week.
CNN reached out to HBO, which did not comment on the matter. (CNN and HBO are owned by the same parent company, WarnerMedia.)
The HBO drama has filmed in parts of Northern Ireland for scenes before, including the Red Wedding and the Battle of the Bastards.
HBO previously said Naomi Watts will play “a charismatic socialite hiding a dark secret” in the project from creators Jane Goldman and George R.R. Martin.
The series will be set thousands of years before the events already seen in the “Thrones” series. It will follow the world’s “descent from the golden Age of Heroes into its darkest hour,” a description read.