The "Game of Thrones" spinoff will begin filming in the fall.
The spinoff, which has a tentative title of "The Long Night," will film at The Paint Hall at Titanic Studios, according to the Belfast Telegraph.
HBO has previously used the studio to film "Game of Thrones."
"Game of Thrones" is based on George R.R. Martin's "A Song of Ice and Fire" book series, and will return for an eighth and final season on HBO in 2019.
"Yes, it is true, after more than a year of development, HBO has greenlit the first of the 'Game of Thrones' successor shows that we've been working on," Martin confirmed in a blog post.
Martin said "The Long Night" will take place 10,000 years before the events of "Game of Thrones."
"Yes, this is a prequel, not a sequel," Martin added. "None of the characters or actors from 'Game of Thrones' will appear in the new show."