By David Sillito
BBC Arts correspondent
More than one thousand chanting and singing fans have gathered in London to meet the cast of High School Musical 2.
The cast have grown accustomed to being the centre of attention
Stars of the made-for-TV family movie, including lead actors Zac Efron and Vanessa Hudgens, attended the event at HMV's flagship store on Oxford Street.
"You can never get used to it, it's an adventure," said Efron, who plays school basketball captain Troy Bolton.
The film's debut broke TV viewing records in the US last week. UK viewers can see it on Disney on 21 September.
Despite the crowds in London, many passers-by were baffled as to what High School Musical was all about.
It began life as a low-budget movie on the US Disney Channel, one of ten such films the company produces every year.
Vanessa Hudgens, who plays the shy, academic Gabriella Montez, was just pleased to have got a part.
"I'd been out of work for a year and I just thought: 'Oh wow - musical!'" said the 18-year-old actress.
Hudgens, along with the rest of the cast, had no idea that High School Musical would turn into something more than just a few weeks' work.
Fans filled the store to catch a glimpse of their heroes
The plot is a familiar one - sporty Troy falls for clever Gabriella despite their different backgrounds. There are a few ups and downs, and a lot of singing and dancing.
It is Grease for the noughties but even more innocent.
But something about the show caught the imagination of its pre-teen audience.
The soundtrack became 2006's biggest-selling album in the US and led to a series of huge stage shows.
On YouTube there are dozens of clips - many featuring fans performing the songs themselves - and around the world, schools are starting to put on their own versions of the show.
In all, Disney is thought to have made about $100m (£50m) on the film, which cost just $4m (£2m) to make.
"You can never get used to it, it's an adventure," says 19-year-old Efron, who has become a heart-throb after his starring role.
Hudgens is equally overwhelmed. "Once it started to blow up it was just insane, it really hasn't sunk in yet," she says.
Word of mouth
But in an era where all ages seem to be listening to the same music, how has this phenomenon sneaked under the radar?
Zac Efron and Vanessa Hudgens have become the film's idols
One answer is the now fragmented nature of television.
The original movie was made for and shown by the Disney Channel, becoming a word of mouth hit in the playground.
And while the sequel may have broken viewing records for a cable channel in the US last week (17.2 million tuned in at one point) it has remained largely a teen-only cult.
The zesty, upbeat songs have received relatively little airplay on mainstream radio, yet more than three million albums have been sold. Press coverage has also been rather thin - this is a phenomenon of multi-channel TV, the internet and live events.
Of course, the question with all teen crazes is: how long will it last? Disney clearly has long-term plans for the franchise - with more than 100 tie-in products, ranging from shoes to backpacks, due to hit stores in time for Christmas, while an ice-skating spin-off launches next month.
And High School Musical 2, with its story about summer jobs, will be followed by a cinema release of the final chapter, in which the students graduate.
After all, the cast cannot remain high school students forever.