Image copyright AP Image caption Augustus (Ansel Elgort) and Hazel (Shailene Woodley) meet at a cancer support group

Teen romance The Fault in Our Stars trounced Tom Cruise's latest action movie when it opened at the US box office; now it's time for the UK's cinemas to be flooded with tears.

It is not much of a spoiler to reveal that, unlike many recent Young Adult books-turned-movies, The Fault in Our Stars does not feature any vampires (Twilight), or take part in a dystopian universe (The Hunger Games).

However, the love story of 16-year-old Hazel Grace Lancaster (played by Shailene Woodley) and Augustus Waters (Ansel Elgort), who meet at a cancer support group, has become a phenomenon.

People can relate to a love story. Everyone wants a beautiful love with someone Ansel Elgort, Augustus in The Fault in Our Stars

The book has sold more than nine million copies, more than 23 million people have watched the film's trailer and it took $48.2m (£28.7m) in its opening weekend at the US box office, leaving Tom Cruise's big budget blockbuster Edge Of Tomorrow trailing with just $29.1m (£17.3m).

Its success, says Elgort, is down to the fact that it's a "real story".

"You know people do like stories about vampires and there are very successful franchises and TV shows based on them or dystopian worlds.

"But young people [also] want stories that aren't fantasy, that are real and they can really relate to, because it's very close to themselves," he says.

Human beings

Author John Green was inspired to write the book after working as a student chaplain in a children's hospital, and it is dedicated to his friend Esther Earl, who died of thyroid cancer in 2010, aged 16.

The story doesn't shy away from the realities of cancer - Hazel wears an oxygen tube throughout the film, and Gus has lost a leg from the disease.

Image copyright AP Image caption Author John Green calls his millions of Twitter followers "Nerdfighters"

Elgort says he spent time researching his role with young cancer patients.

"The most important thing was just making him a real person, a regular guy and not playing his sickness," says Elgort.

"These characters, Gus and Hazel, they're so relatable because they're human beings - they're not cancer."

Green didn't write the screenplay - leaving the business of adapting his book to Scott Neustadter and Michael H Weber, who had a cult hit with indie romcom (500) Days of Summer - but he spent a lot of time on set, filming and tweeting from behind the scenes.

Image caption Angelica and Merrou were among hundreds of fans at an event in London this week

His own brief cameo was cut by director Josh Boone, but Elgort says his presence gave the cast "a lot of confidence".

Many have likened the author's status to that of a rock star, with 2.6 million followers on Twitter, who he calls his "Nerdfighters", and a YouTube channel, which he runs with his brother.

He has even been credited with "saving" Young Adult literature and the fans are certainly passionate.

A meet the cast event at The Apple Store on London's Regent Street attracted hundreds earlier this week, many queuing up from first thing in the morning.

Angelica, 17, had spent three hours making a shirt emblazoned with her favourite quotes from the book.

"It's not just one of those love stories. The characters are so intelligent and witty," she explains, having read the book "seven times this year, three times last year and a time before."

"It's one of those things that I can't even explain," she adds. "It's got me through so much."

Elysia, 14, is quick to dismiss the idea of "Sick Lit" as a booming Young Adult genre, claiming "it's just this story" that fans are interested in.

"It makes us feel the same way that [Hazel] feels about him (Augustus). It makes us sad, and at the same time it makes us happy," she says.

Image copyright Handout Image caption Elgort (left with Nat Woolf who plays Issac and Woodley) stuck as close to the book as possible

One fan called the character of Augustus Waters "the love of her life", and Elgort admits there was pressure to live up to the Gus readers have created in their minds.

"I was worried when I first started. He's so important to a lot of people who love him and were affected by him and the story - I didn't want to mess him up," says the actor.

"He's written in a certain way and that's the way I was going to portray him. I just wanted to stick as close to the book as possible."

That hasn't stopped some finding flaws in Elgort's performance, but he says he's happy with it.

"Even if I got a negative tweet or something, 'Oh you're a terrible Augustus', I wouldn't be offended at this point because I'm happy with my work and a lot of people are."

His performance has certainly had an impact. Tearful fans write about how to deal with their "cry-hangovers" and tell Twitter how many tissues they needed to get through a screening.

"Just seen The Fault In Our Stars," tweeted singer Nina Nesbitt after the UK premiere. "Swimming home in my own tears."

Image copyright AP Image caption Elgort and Woodley previously starred together in Divergent

For fans who have had cancer themselves, the story is especially moving.

Merrou, who is 17 and in remission from leukaemia, brought a sign she'd made to Monday's fan event. It read: "This film means everything to me because I am a cancer survivor".

"In some sort of crazy way I feel like John Green has got in my head and written a book that I get," she tells the BBC.

"Although it is such a sad story, it's helped me through so much as well.

"You feel very helpless and I think that he really captures that in the book. Even though it is make believe, he definitely got it right. He got me right."

Elgort acknowledges cancer is "a big theme in the movie", but he says that's not the only reason the story has touched so many people.

"Everyone is touched by cancer in their life, that's why people can relate to the story. [But] then it is also just a love story.

"Everyone wants a love story. Everyone wants a beautiful love with someone."