Max Martin "tortured" Kelly Clarkson in order to get 'Since U Been Gone' perfect.
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'.
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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'."
This article originally ran on celebretainment.com.