Anne Groell, the editor of George RR Martin's epic book saga A Song of Ice and Fire which is being filmed for TV as Game of Thrones, has suggested that the series might end up with eight novels rather than the planned seven.

In a Q&A with fans, she said that the series was originally a trilogy, before she cajoled Martin into writing more:

"I remember when he called me, years and years back, to confess that his little trilogy was…well…no longer a trilogy. He predicted four books. I said Seven Books for Seven Kingdoms. Then he said five books. I said Seven Books for Seven Kingdoms. Then he went to six. I said… Well, you get it. Finally, we were on the same page. Seven Books for Seven Kingdoms. Good. Only, as I recently learned while editing The World of Ice and Fire (another awesome thing you must buy when it comes out!), there are really technically eight kingdoms, all having to do with who has annexed what when Aegon the Conqueror landed in Westeros. So, maybe eight books for Seven Kingdoms would be okay."

She admits that "7 [books] is what we currently have under contract," and that she is currently working with him on the "amazing" sixth book, The Winds of Winter, which isn't completed: "When I have a [publication] date, you will have a date." The World of Ice and Fire which she alludes to is a forthcoming companion book outlining the gigantic setting for the saga.

Jane Johnson, his UK publisher, told the Guardian: "I know there's been some speculation that A Song of Ice and Fire may run to more than the seven books we currently have under contract, but in all honesty only George knows how many books there will be in the series and he's not saying: indeed at this stage of the writing, with the many branching pathways of the characters' stories still to intersect, he may not know. As an editor I can say that it feels as if there's a lot to tie up in just two more novels – albeit very long novels – but if George continues to kill off characters in his usual ruthless fashion it could easily be over in the planned seven books!"

The most recent instalment, A Dance With Dragons, was published in 2011, but the success of the TV show in the interim means that anticipation for the next is higher than ever. Martin is famous for spending a long time between books, frustrating fans eager for the next instalment, who have written (sometimes abusive) comments on his blog and elsewhere telling him to continue writing the series. "The more readers you have, the harder it is to keep up, and then you can't get any writing done," Martin has said. Neil Gaiman was moved to write "George RR Martin is not your bitch" on Twitter, when he was quizzed about the progress of the novels.

When asked whether she'd tried to get Martin to work on the road as he meets fans, rather than only on his computer at home, Groell replied: "Good gracious, yes! Multiple times. He is one stubborn man, and very set in his ways, though."