The author, speaking at Edinburgh film festival, revealed that some fans already know the ending, as he left small clues in the books:

“So many readers were reading my books with so much attention that they were throwing up some theories and while some of those theories were amusing bull— and creative, some of the theories are right. At least one or two readers had put together the extremely subtle and obscure clues that I planted in the books and came to the right conclusion…I’ve wrestled with this issue, because I do want to surprise my readers. I hate predictable fiction as a reader, I don’t want to write predictable I wrestled with that issue and came to the conclusion that changing it would be a disaster, because the clues were there. You can’t do that, so I’m just going to go ahead. Some of my readers who don’t read the boards, which thankfully there are hundreds of thousands of them, will still be surprised and other readers will say “see, I said that four years ago, I’m smarter than you guys.”

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