The show will be set thousands of years before the events of HBO's award-winning drama, when the world of Westeros was young.
HBO is moving ahead with a Game of Thrones prequel, the first of five potential spin-off projects.
The company has given a pilot order for a prequel set thousands of years before the events of the Game of Thrones television show.
Depending on the quality of the pilot, the network will commission a full series.
Although untitled at the moment, the prequel was created by British screenwriter Jane Goldman alongside the author of the novel series, George RR Martin.
It will cover a different period than George RR Martin's new book, Fire and Blood, which is being released in November this year.
The book - which is an imaginary history, rather than a novel - is set 300 years before A Game of Thrones, "when dragons ruled Westeros".
The eighth and final season of Game of Thrones is due to be broadcast in 2019.