Author George R.R. Martin said he was "surprised" by the number of Game of Thrones spinoff series planned by HBO.

Discussing the idea of four prequels, Martin said, "It surprised me, I’ll admit that... I'd never heard of that before. I thought we'd be going ahead with one, with one development, with the one that I pitched to them, the Dance of the Dragons idea." This was one of several statements the author made in interviews featured in the book, Tinderbox: HBO's Ruthless Pursuit of New Frontiers, by James Andrew Miller.

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House of the Dragon, a series based around House Targaryen, is due to air in 2022 and this idea was suggested by Martin himself after another suggestion was shot down. "They didn't like the Dunk and Egg idea because they were familiar with the novellas — somebody there had read them — but it was too soft," Martin said. "But they did respond to the Dance of the Dragons idea." The novel Dance of the Dragons became the basis for House of the Dragon.

Game of Thrones was adapted from Martin's A Song of Ice and Fire book series and Martin remained highly involved in the development of the show, penning the screenplays for several episodes including "The Pointy End" and "Blackwater." Despite this level of involvement, he was still surprised at how many shows HBO intended to add to the Game of Thrones universe. "Then I suddenly found out that they had put four prequels in motion," Martin said. "The Dance of the Dragons idea was just one of them."

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Earlier this year, it was reported only one Game of Thrones spinoff was still in active development. A prequel series was planned as far back as 2018 but the series was pulled, despite HBO spending $30 million on shooting the pilot episode in 2019.

Animation seems to be a popular source for Game of Thrones shows as other reports suggest HBO has three Game of Thrones inspired animated shows in development. The only one named and identified so far is a show centered on the The Golden Empire of Yi Ti, a highly advanced and civilized region in Essos.

House of the Dragon stars Paddy Considine, Matt Smith and Emma D'Arcy and is due to air on HBO in 2022.

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Source: Tinderbox: HBO's Ruthless Pursuit of New Frontiers, via Insider