One afternoon in March 2012, Simon Cowell was taking a cigarette break backstage at Greensboro Coliseum in North Carolina, where he was judging auditions for the American X Factor, when he came across a girl lying on the ground, sobbing.

The girl was Camila Cabello. She had just turned 15, and for her birthday had asked her parents – Cuban immigrants living in Miami, who were making ends meet as a shop assistant and car washer – to drive her the 12 hours from their home to the auditions. Cabello explained to Cowell that, having been kept waiting for two days to see the judges, she had just been told by the producers that time had run out and she should go home.

“Apparently she was a reserve,” Cowell tells me over the phone. “So I said to her, ‘Listen, I’ve got no idea what you’re talking about, or what a reserve is, but since you’re here, come and audition.’ Five minutes later, she sang [Aretha Franklin’s Respect] in front of 7,000 people, and it was sensational.”

Cabello has a pint-size frame and a gigantic, intoxicating voice. What it lacks in technical finesse it makes up in youthful passion and romantic melodrama. Cowell installed his charismatic young discovery as the (unofficial) lead singer of a group comprising four other female contestants, and Fifth Harmony was born. After finishing the competition in third place, they signed to Cowell’s Syco label, becoming a sort of sister act to his other X Factor protégé group One Direction. Within months, Fifth Harmony had racked up a platinum-selling debut album of chart-friendly feminist anthems, a sold-out world tour, two performances at the White House and tens of millions of young fans.