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House of the Dragon will take place 300 years before the events of Game of Thrones, a medieval fantasy series that became a global phenomenon before it ended its eight-season run in May this year.
The new series will be based on Martin's book Fire & Blood and will tell the story of House Targaryen, HBO said.
The network announced House of the Dragon at an event on Tuesday intended to stir enthusiasm for HBO Max, a streaming service that will launch in May 2020 at $US15 ($NZ23) per month to compete with Netflix Inc and Walt Disney Co.
HBO did not say when House of the Dragon would become available.
Watts' prequel gets cut
Earlier in the day, Hollywood publications reported that HBO had scrapped plans for a Game of Thrones prequel starring Naomi Watts.
A source familiar with the decision confirmed the reports were accurate. The reason for the decision was unclear.
A pilot, or first episode, for the show was shot in Northern Ireland earlier this year. The story was set thousands of years before the events covered in Game of Thrones.
Casey Bloys, president of programming at HBO, had told reporters in July after filming finished on the pilot episode that he was pleased with what he had seen.
"It looks really good. The cast was amazing," Bloys said at a Television Critics Association event in Beverly Hills.
The final season of "Game of Thrones" won 12 Emmy awards, including the top prize of best drama series, in September.
The pilot for the prequel was one of several "Game of Thrones"-related projects that were put into development at HBO prior to the end of the series.