The sixth installment in the "A Song of Ice and Fire" series, "Winds of Winter," will not be completed by the start of the next season of Game of Thrones -- meaning the sixth season of the hit HBO series will spoil the future of the books.

Author George R.R. Martin explained over his "Best of Times, Worst of Times" blog series:

"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 And that almost certainly means that no, THE WINDS OF WINTER will not be published before the sixth season of GAME OF THRONES premieres in April (mid April, we are now told, not early April, but those two weeks will not save me)."

Martin commented on the show's fifth season, which diverged from the books because it inevitably caught up to the series:

"Look, I never thought the series could possibly catch up with the books, but it has. The show moved faster than I anticipated and I moved more slowly...Given where we are, inevitably, there will be certain plot twists and reveals in season six of GAME OF THRONES that have not yet happened in the books. For years my readers have been ahead of the viewers. This year, for some things, the reverse will be true."

As for the degree of spoilers we'll encounter in "Game of Thrones" Season 6, Martin says:

"When you ask me, 'will the show spoil the books,' all I can do is say, 'yes and no,' and mumble once again about the butterfly effect. Those pretty little butterflies have grown into mighty dragons. Some of the 'spoilers' you may encounter in season six may not be spoilers at all... because the show and the books have diverged, and will continue to do so..."

Martin was very apologetic for missing the deadlines -- which he fully takes the blame for -- but ended the post with a promise that he'll continue writing, "Page at a time."

"Games of Thrones" returns to HBO for its sixth season in April.