George RR Martin told fans today that the long-awaited sixth volume in his Game of Thrones fantasy series, The Winds of Winter, would not be published this year – but softened the blow by revealing that his “imaginary history” of the Targaryen family in Westeros would be released on 20 November.

Fire and Blood is set 300 years before the events of A Song of Ice and Fire and, said its publishers Bantam and Voyager, will chronicle “the Targaryen civil war that nearly ended their dynasty forever”. In a post on his blog, Martin described the book as his “the GRRMarillion (or the first half of it, at least); that is to say, my version of Tolkien’s mammoth history of Middle Earth”, and revealed it ran to almost 1000 manuscript pages. He first mentioned the volume, the first of a planned two histories of Westeros, last summer, saying at the time that he was not sure if it, or The Winds of Winter, would be released first in 2018.

Today, he confirmed that fans would have to content themselves with the history, for this year at least. The fifth book in the sequence on which the hit HBO series Game of Thrones is based, A Dance With Dragons, was published in 2011, with the television series now taking Martin’s characters far beyond the places they have reached in the books.

“No, winter is not coming … not in 2018, at least. You’re going to have to keep waiting for The Winds of Winter. You will, however, be able to return to Westeros this year,” Martin said today.

He stressed to fans that the book was not a new slice of narrative fiction set in the Game of Thrones world. “I do want to stress... indeed, I want to shout... that Fire and Blood is not a novel. This is not a traditional narrative and was never intended to be… let’s call this one ‘imaginary history’ instead. The essential point being the ‘history’ part. I love reading popular histories myself, and that’s what I was aiming for here,” he wrote on his blog. “So: not a novel. Everyone clear on that? (Though there are enough stories here for twenty novels. Battles, bloodshed, betrayals, love, lust, horror, religious wars, politics, incest, historical revisionism, all the fun stuff).”

The book, he revealed on his blog, would cover “all the Targaryen kings from Aegon I (the Conquerer) to the regency of Aegon III (the Dragonbane), along with their wives, wars, siblings, children, friends, rivals, laws, travels, and sundry other matters … Oh, and there are dragons too. Lots of dragons.”

Voyager and Bantam described the book as the “definitive history of the Targaryens in Westeros”. “Readers may have glimpsed small parts of this narrative before, in The World of Ice and Fire and various anthologies, but the full tapestry of Martin’s history of the Targaryens is revealed here for the first time,” said the publishers, who will release the book on 20 November, with 75 new illustrations from the artist Doug Wheatley.

Martin did not reveal if the prequels to Game of Thrones which are currently being developed by HBO would be based on material from Fire and Blood. “It’s a logical question. The only answer I can give is… ah, well, no one is sure yet, and anyway, I am not allowed to say. So let’s move that to the side,” adding: “As for me, I’m returning once again to The Winds of Winter.”