Author says he feels he has failed his fans because new HBO TV series will be shown before its source material

The author of the Game of Thrones series, George RR Martin, has confirmed he missed the last deadline that would have allowed the sixth novel in his fantasy series to be published before the next TV series begins.

The failure to meet the 31 December deadline will mean the sixth season of HBO’s Game of Thrones series will appear on screen before its source material.

Martin has been working closely with HBO writers and producers to help the series mirror the books, but the next season is due to start in early 2016 and Martin’s sixth book, the Winds of Winter, will not be ready.

Announcing an update on the progress of his book on his blog early on Saturday, Martin prefacing his announcement with the words “you won’t like it”. He wrote: “For months now I have wanted nothing so much as to be able to say, ‘I have completed and delivered The Winds of Winter’ on or before the last day of 2015. But the book’s not done.

“Nor is it likely to be finished tomorrow, or next week. Yes, there’s a lot written. Hundreds of pages. Dozens of chapters. But there’s also a lot still left to write. I am months away still … and that’s if the writing goes well. (Sometimes it does. Sometimes it doesn’t.)

“Chapters still to write, of course … but also rewriting. I always do a lot of rewriting, sometimes just polishing, sometimes pretty major restructures.”

Martin said he and his editors had met HBO producers in early 2015, after the fifth series of Game of Thrones aired, to discuss how The Winds of Winter could be out before the next season. He said that for the book to be out in March 2016 he would have to deliver the manuscript in October, which “seemed very doable to me. In May”.

He said a busy year meant he would be unable to meet the deadline, which deeply depressed him. Explaining the reaction of his editors, the author said: “[I] thought they’d be sick about it … but I have to say, my editors and publishers are great, and they took it with surprising equanimity.”

A new deadline of New Year’s Eve was agreed and has since been missed, forcing Martin to admit: “Here it is, the first of January. The book is not done, not delivered. No words can change that. I tried, I promise you. I failed.

“I blew the Halloween deadline, and I’ve now blown the end of the year deadline. And that almost certainly means that no, The Winds of Winter will not be published before the sixth season of Game of Thrones premieres in April.”

Apologising to fans of the books, for whom he accepted some aspects of the TV show would spoil events in the new novel, he said: “I won’t make excuses. There are no excuses. No one else is to blame. Not my editors and publishers, not HBO. It’s on me. I tried, and I am still trying.”