When the teen-vampire drama Twilight first hit the big screen in November 2008, its romantic tale of passionate first love earned it masses of adolescent, female fans.
It also, however, found an unexpected audience in middle-aged women. One such was Erika James, or E L James as she is now known to the quarter of a million readers who have fallen for her erotic fiction trilogy, 50 Shades Of Grey, which has just been acquired by Random House.
"I saw Twilight in November 2008 and I loved it. For Christmas, I asked my husband for the books and I sat down to read them and emerged five days later. I loved it."
James was so inspired she wanted to try her hand at writing a love story of her own. She sat down on January 15 and started her first novel. "I finished it in April. It was really badly written but I'm revisiting it because it's a great idea."
By August that year, she had finished a second book. In her quest to satisfy her hunger for the Twilight saga stories, she came across some fan fiction on the web -- fan-penned spin-off stories about favourite characters, often with an added sexual element.
Inspired again, James wrote a 70,000-word fan-fiction story based on the characters from Twilight and, because a lot of fan fiction incorporates an erotic element, she began thinking about a BDSM (Bondage-Dominance-Sado-Masochism) story.
The result is her trilogy 50 Shades Of Grey, which has been bought for a seven-figure sum. The film rights are also being sold and negotiations are rumoured to be at the €5m mark.
And all for the story of a 21-year-old graduate student, Anastasia Steele, who falls in love with a billionaire, Christian Grey, with a taste for dominating his sexual partners.
The books were initially published by a small, independent publishing house in Australia and became a word-of-mouth hit with women of a certain age, which led to the books being dubbed 'mummy porn'. To this reader, though, they seemed like standard bonkbuster material.
"Of course, this stuff has always existed," says James. "I don't understand the reaction. Yes, it has sex in it but when people fall in love they have sex . . . in my humble experience," she adds.
But do they have BDSM sex? "It's a fascinating world. I did a huge amount of research," she laughs.
One of the explanations offered for the success of the book is that it began life as an internet story and then an eBook, which enables people to read erotic fiction on the bus or train without fear of judgment. James certainly thinks it played its part.
"I used to read a lot of romantic fiction, especially during my commute to work, and I'd be mortified on the tube, trying to hide the cover. I think the advent of the e-book has enabled women to read it."
Why do women like to read this kind of erotic story? "It's just something that people will enjoy and get lost in. It's a fantasy world and I just wanted to explore that and see what first love is again. You get to a certain age and that's not going to happen again."
Fantasy has always been the point of romantic or erotic fiction but some feminists have criticised James's novel because of the sexually dominant 'hero', but James is not buying it.
"Women have always liked archetypes of dominant men, that harks back to the Mr Rochester character.
"It's nobody's business what people do safely, sanely and consensually behind closed doors," she adds.
Thanks to 50 Shades Of Grey's demure jacket, you won't have to read it behind closed doors.
50 Shades Of Grey is published by Random House.