Deafening screams from hundreds of fans chanting 'We want BAM!', roared through the Mander Centre as the pint-sized popstars met fans and signed album covers and posters at HMV.
The mostly teenage girls, or 'Bambinos' as they've been dubbed, queued for hours waiting for their idols to show, with many screaming as the duo arrived.
And HMV staff said yesterday's event was one of the band's busiest ever in-store signings.
The singing and rap duo, made up of 14-year-old Leondre Devries, aka 'Bars' and 16-year-old singer Charlie Lenehan, aka 'Melody', shot to fame on Britain's Got Talent in 2014 after head judge Simon Cowell pressed the 'golden buzzer', guaranteeing them entry to the semi finals.
They finished in third place and after the show signed a record deal with Syco Music.
Their debut single, Hopeful, was released in July 2014 and their debut album, 143 was released on Friday.
Among the 300 fans lining up to see the stars yesterday was 12-year-old Lauren Steadman, from Bradley, Wolverhampton.
She said: "They are so good, I listen to them all the time, I absolutely love them.
"I've been here since 8am and I would have waited longer if we had to.
"They're always really good to their fans and every time I've seen them they take time out to make us feel loved."
Events planner for HMV, Laura Thomas, said: "These are by far the biggest queues we've seen.
"Parents have been dragged down here but I'm sure a few of them are enjoying it just as much as their kids. People have been queuing since 7am, which is bonkers."
The boys use their lyrics to inspire others, with songs drawn from experiences of bullying.