Eminem and Gwen Stefani joined forces for “Kings Never Die,” which dropped Friday and will be found on the soundtrack for the boxing drama Southpaw — and while Stefani says she’s always wanted to work with the rapper, her voice almost didn’t cooperate when it came time for their collaboration.

“The process was really simple,” she told EW on Friday while hosting the Harajuku Lovers Tea Party at BeautyCon Los Angeles. “One of his guys came and played me the song and then I was like, ‘Yeah, I like it! Amazing!’”

“I’ve always wanted to work with him — he’s a genius — and then all of a sudden they called me and said, ‘It has to be done today’ and I was like, ‘Ah, my voice’ — I had a cough or something,” she recalled. “I went in and I made it happen, but it was like, barely.”

“It was like, ‘God, why does today have to be the day my voice is not happening?’ But it ended up turning out good,” Stefani added. “I wanted to do something with him for so long and I feel honored — he’s very selective. I feel really honored.”

Southpaw and its soundtrack will be released July 24. Take a listen to “Kings Never Die” below.