https://www.theguardian.com/books/2019/oct/31/george-rr-martin-wont-write-spinoffs-game-of-thrones-book-finished-house-of-the-dragon-winds-of-winter

As TV prequel House of the Dragon is announced, author says finishing The Winds of Winter, the sixth volume of his saga, ‘remains my priority’

George RR Martin has promised not to write any scripts for HBO’s new prequel show based on his imaginary history of the Targaryen family until he has “finished and delivered” The Winds of Winter, the long-awaited sixth book in his A Song of Ice and Fire series.

Hours after the bloody world of Game of Thrones claimed another victim – a TV prequel set thousands of years before Martin’s books that has been scrapped – television network HBO gave the green light for a full 10-episode season called House of the Dragon, another prequel spinoff but focused on the brutal and fiery Targaryen dynasty.