The latest instalment of EL James's sadomasochistic Fifty Shades Of Grey saga has been released in a flurry of publicity and copies are already flying off the shelves.
The new book, called Grey, is a re-telling of the first novel in the hit series about an affair between mysterious tycoon Christian Grey and lover Anastasia Steele from the point of view of its title character.
Eager readers downloaded the eBook version shortly after midnight rather than wait for the shops to open with fans tweeting their joy at getting their hands on the book early.
Sarah Thomson said: "Started reading Grey soon as it downloaded - don't see much sleep for me tonight."
And Sarah Roche tweeted: "I'll be awake all night reading on the Kindle."
Meanwhile, fellow erotic novelists joined in as they ploughed through the plot.
Divas writer Rebecca Chance tweeted: "Stay with me twitter people as I live tweet Grey! It's already epic."
Wendy Leigh said: "EL James am 10% into Grey & love the intimate close-up perspective on the real Christian Grey."
The story, set over the course of a month from May 9 2011 to June 9 2011, is described as "a fresh perspective on the love story that has enthralled millions of readers around the world" and the story of the title character's battle with the "compulsion to control" and "dark sexual desires".
It starts with the title character having a nightmare about his childhood before he meets Steele who is described as arriving in a "a whirl of long chestnut hair, pale limbs and brown boots".
The story of Grey's pursuit of Steele and James's raunchy description of their S&M relationship will be familiar to readers of her first three books who are likely to make this one a worldwide best-seller as well.
A review for the Daily Mirror said "there's absolutely nothing vanilla about this book".
Fans have already started handing over cash at the tills for hard copies of the book, with Waterstones fiction buyer Chris White saying: " The early signs are that Grey may be as big as the original. It's selling so quickly we've already ordered more stock."
The book is dedicated by James to her readers with the words: "Thank you for all that you've done for me. You rock my world every day" and includes thanks to a host of people including those who guided the author through "an education in soil science", "behavioural health" and "guidance in flying a helicopter".
James is in New York for the publication day, which is the birthday of the fictional Grey, and a billboard wishing him a happy birthday has gone up in Piccadilly Circus, central London.
The book made headlines last week ahead of its publication when it was reported a finished copy had been stolen.
The publishers vowed to continue to investigate the theft of a copy of the unpublished book despite police saying there was "no evidence" a crime was committed.
Jamie Dornan played Grey and Dakota Johnson was his lover in the hugely successful film version of the story.
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.