For Spears, working with perfectionists suited her. “I really respect that when I’m working with him,” she says. “I think Max ( Max Martin ) is a genius. It all just came together and felt right. In my opinion Max is the greatest songwriter of all time.”

Another person to witness firsthand this studied effortlessness was Nana Hedin, a backing vocalist who had previously worked with Denniz Pop on songs by Dr Alban, whose 1992 hit It’s My Life soundtracked a Tampax advert in the UK. Pop recommended Hedin to Martin, who brought her onboard for …Baby One More Time. “I remember I thought the song was for teenagers but the production was filled with a grown-up attitude and sounds that I really liked,” she says. “I was so impressed by how a guy like Max could write lyrics that got into the hearts and spoke to the teenage thinking.” Occasionally, Hedin would record her backing vocals first, before the artist arrived, but with …Baby One More Time Spears’s vocals were already recorded. “I tried to sound exactly like her,” she laughs. “It was hard, but a lot of fun. I’m like a parrot in many ways. I try to get the same vibe and use the exact same pronunciation as the artist. In one harmony, each take is different; I sing very high, in another I use powerful belting, the next I’m whispering and sometimes I even pinch my nose for a sharper sound.”