EL James' publisher has said it will not rush to release her latest novel despite fears pirated versions could appear after a copy of the sado-masochistic tale was stolen.
The book, titled Grey, is a reworking of the original Fifty Shades Of Grey which was a worldwide bestseller and inspired a hit film and a surge of erotic novels.
James has rewritten the book, about an affair between the mysterious tycoon Christian Grey and lover Anastasia Steele, from the point of view of its title character.
A spokeswoman for Penguin Random House said: " Grey will be published on June 18 - Christian Grey's birthday - as planned. We can confirm that the Kent police are investigating the theft of a finished copy of EL James's new book Grey. We will not be issuing any further statement."
Jamie Dornan played Grey and Dakota Johnson was his lover in the film version of the story.
James said she wrote the book after huge demand from fans. On the opening page, she says it is "dedicated to those readers who asked ... and asked ... and asked ... and asked for this".
The Fifty Shades trilogy - Fifty Shades Of Grey, Fifty Shades Darker and Fifty Shades Freed - has sold more than 125 million copies around the world.
It has made James a millionaire many times over. This year's Sunday Times Rich List estimated her fortune at £75 million.
A spokesman for Kent Police said: " Officers are making inquiries after receiving a report that a book had been stolen on June 8."