The Swedish producer - who has masterminded hits for likes of Britney Spears, Taylor Swift, Katy Perry and Backstreet Boys - has revealed that he had a "particular way" in which he wanted to the vocals to sound like and despite Kelly singing it "amazingly" he got her to re-do it several times to get it just right.

Max - who co-wrote and producer the song - told BBC Radio 2: "She came in and sang the song amazingly, she killed it.

"But I had this particular way you had to ... I tortured her for a minute."

The 'Because of You' hitmaker ended up winning the Grammy for Best Female Pop Vocal Performance with the 2004 hit, which featured on the 'American Idol' winner's debut album 'Breakaway'.

Max added: "She was such a super girl and I think the song was maybe not what she was normally doing.
"I think she was more of a big ballad girl, so yeah that turned out so amazing."

The songwriter credits working with people like Kelly with transforming his career.

Meanwhile, the producer previously praised Katy Perry - who worked on 2013's 'Roar' with - for creating songs that become "bigger than just a song".

He said: "When pop culture can influence things in any way, when a song becomes something bigger than just a song, that's the greatest thing to me.

"I saw the video where the whole staff of a children's hospital sang 'Roar', and it was a reminder for me. I have a tendency to belittle what I do. I think it's a consequence of trying to keep the ego in check. I go, 'What the f**k are we doing all day when others are working for equality, Syria, battling cancer.' But then something like this happens; a song finds its way outside the studio and comes to really mean something to people.

"It's not every time that I'm proud of a tune, but I am when it comes to a song like 'Roar'."