Martin has worked for eight years to finish his sixth book, The Winds of Winter, and still has no publication date.
His last book, 2011's A Dance with Dragons, ended with the death of Jon Snow.
Martin has explained to showrunners David Benioff and Dan Weiss how he plans to ends the story but the scriptwriters have often changed parts of the books, including Ramsay Bolton marrying Sansa Stark whereas in the books he marries a minor character.
"(The concern) used to be that the books would spoil the show for people — and luckily it did not for the most part," Benioff says.
"Now that the show is ahead of the books, it seems the show could ruin the books for people. So one thing we've talked to George about is that we're not going to tell people what the differences are, so when those books come out people can experience them fresh."
Martin says while he has "mixed feelings" about the end of the TV show he will not be leaving Cersei Lannister, Daenerys Targaryen and the Stark family behind.
"It's the end for a lot of people," Martin said. "It's not the end for me. I'm still deeply in it. I better live a long time because I have a lot of work left to do."