George RR Martin says she is ''saddened'' by HBO's cancellation of its Game of Thrones prequel show, which was set to star Naomi Watts.

It was announced this week that the TV network had axed plans for a prequel to the hit fantasy series, which was based on the A Song of Ice and Fire book series by 71-year-old Martin, after the pilot episode was not picked up for a full series.

Martin has said he's ''heartbroken'' by the decision not to continue with the series, which was supposed to be set thousands of years before the main show.

Writing on his blog, 'Not a Blog' blog on Wednesday, the author said: "As exciting as the series order is, I would be remiss if I did not also mention the bad news.

"HBO also announced that it has decided not to proceed with the other successor show we had in development, the one I kept calling The Long Night (though it was, and remains, officially untitled), the pilot for which was shot in Northern Ireland last spring and summer.

''Set thousands of years before either Game of Thrones or House of the Dragon, and centered on the Starks and the White Walkers, the untitled pilot was written by Jane Goldman, directed by S.J. Clarkson, and starred Naomi Watts, Miranda Richardson, and a splendid cast. It goes without saying that I was saddened to hear the show would not be going to series.''

Martin admits the show cancellation had nothing to do with House of the Dragon, which will focus on the Targaryen household, but says he doesn't know why the channel didn't pick up both shows.

''Jane Goldman is a terrific screenwriter, and I enjoyed brainstorming with her. I do not know why HBO decided not to go to series on this one, but I do not think it had to do with 'House of the Dragon'. This was never an either/or situation," he added.

''If television has room enough for multiple CSI's and Chicago shows ... well, Westeros and Essos are a lot bigger, with thousands of years of history and enough tales and legends and characters for a dozen shows.''

Martin reckons he believes everyone involved with the show is ''feeling the disappointment'', adding: ''Heartbreaking as it is to work for years on a pilot, to pour your blood and sweat and tears into it, and have it come to nought, it's not at all uncommon. I've been there myself, more than once.

"I know Jane and her team are feeling the disappointment just now, and they have all my sympathy ... with my thanks for all their hard work, and my good wishes for whatever they do."

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