The project is top secret, and no details have yet been announced, although producers have told journalists Whitehouse has been cast in a “key role”, though not the male lead.
The Pilot was first announced in June by HBO, with executive producers including current Game of Thrones producer Vince Gerardis, as well as Damages and Bloodline co-creator Daniel Zelman and Jim Danger Gray onboard.
The as-yet-untitled series will reportedly take place thousands of years before the events of Game of Thrones, and will chronicle the end of the Age of Heroes, a period in Westeros history marked by legendary figures like "Bran the Builder" and "Lann the Clever," who were the originators of the Stark and Lannister families.
All other details are being kept under wraps, with HBO only releasing this cryptic description:
“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."
This latest project is reportedly one of many being developed by HBO in the Westeros world, with original creators Jane Goldman and George R.R. Martin involved.
Executives at the network have said that not all scripts will move beyond development, but that this one has been greenlit.
The successor show will not air until at least a year after the eighth, and final, season of Game of Thrones screens in the first half of next year.