Game Of Thrones author George R.R. Martin has missed a December 31 deadline to finish The Winds Of Winter, the latest book in his fantasy series.

That means the HBO season based on that sixth novel will start airing in April, while he is still writing.

The words "you won't like it" appeared on Saturday on Martin's blog, reporting the missed deadline.

Martin said he wanted to say he has delivered The Winds Of Winter for publication, but estimates it will take months more if all goes well.

Martin apologised to fans eagerly awaiting the next instalment of the series in which characters warn of impending doom with the phrase, "Winter is coming". He says he has been working with HBO to ensure the series reflects the as-yet-unfinished book.

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