In a surprise twist to almost no one, author George RR Martin announced that he missed the deadline which would have had The Winds of Winter, Book 6 of the A Song of Ice and Fire book series, published before the airing of HBO's sixth season of the TV series Game of Thrones. 

Martin took to his blog to make the announcement. He wrote: 

“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 And that almost certainly means that no, The Winds of Winter will not be published before the sixth season of Game of Thrones premieres in April.

 

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.” 

This should come as no surprise to book fans, many of whom have been waiting for a completion to this series since 1996. At this time, there is no true end in sight. Book fans will have to look for the TV show to give them an ending. Back in March 2015, show executive producer David Benioff confirmed that the show would spoil the ending of the book series: 

"We know where things are heading," said GoT executive producer David Benioff. "We will eventually meet up at pretty much the same place that George is going. There might be some deviations along the route, but we're heading toward the same destination."

For more info, read more here and here.