The sixth book about the boy wizard will be printed on environmentally-friendly paper.

JK is among a group of writers - also including His Dark Materials author Philip Pullman - who have agreed to start using recycled paper.

So far, the Harry Potter books have used up a whopping 6.5 million trees. At present, no major UK book publishers use 100% recycled paper.

However the situation might change in the future thanks to new recycling techniques from Canada.

They've worked out how to use waste paper from offices to make books, according to a report in The Times newspaper.

The Canadian edition of Order Of The Phoenix was printed without chopping down a single tree.