Bill Sherman, & Juliet’s music supervisor, orchestrator and arranger, tells BBC Culture that collaborating with Martin has been “a daily masterclass in how to write and construct pop songs”. Sherman likens the Swede, who rarely gives interviews and maintains a low public profile, to “the Yoda of pop songwriting”. Together, they’ve “taken Max’s songs apart and put them back together again”, which Sherman concedes is a “strange concept” given how “perfect” the original versions remain. The results are sometimes audacious: ...Baby One More Time has been reimagined as a power ballad, while Can’t Feel My Face is performed as a mash-up with Ariana Grande’s Problem.

A master of hooks

Sherman has spent a considerable amount of time analysing and reconstructing Martin's songs for & Juliet, but says it’s impossible to offer a “convenient one-liner” for what makes them so brilliant. “My day job is musical director on Sesame Street, and what makes a song great for kids is a lot of repetition and what I like to call ‘earworms’ – hooks, things that reel people in,” Sherman says. “It's almost the same thing with Max Martin songs. The verse is a hook, then the chorus is another hook. He's always talking about melody and striving to find that thing that makes it magical.” Sherman says that though Martin sometimes gives off the impression that his songwriting is “some kind of mathematical process”, the thing he says most is: “It just doesn't feel right.”

“He goes a lot on the feel of a song, which seems very subjective to me,” Sherman adds. “But he's been going on his gut for 25 years, and it's hard to argue with his track record.”

At the same time, we know that Martin likes to adhere to certain self-prescribed songwriting rules. New Zealand singer-songwriter Lorde revealed in 2017 that Martin had described her 2012 breakthrough hit Royals as an example of “incorrect” songwriting. “He was basically like, ‘The pre-chorus should be the chorus. That’s the catchiest part of the song,’” she recalled.