Metallica rocker Lars Ulrich was challenged to a street fight by Lou Reed after the veteran singer lost his temper during a heated studio session for their collaborative album Lulu.
The stars formed an unlikely bond and decided to head into the studio to make a record together last year.
Reed previously claimed he had the time of his life working with frontman Ulrich and the band, and credited the relaxed working environment with boosting their creativity.
But not every session went so smoothly and Ulrich reveals he almost came to blows with Reed after becoming embroiled in an argument.
The rocker refuses to disclose the topic of the discussion, but admits he was secretly dreading having to fight the ageing musician because Reed is skilled in martial arts.
Ulrich tells Spin.com, "I had to point something out about how things were functioning in the outside world, (and) he got hot and bothered. He challenged me to a street fight, which is a pretty daunting proposition because he's an expert in martial arts, and is never too far from a sword."
But Ulrich had a back up plan if things really did turn ugly: "The good thing about me is I can do the hundred-metre dash faster than most other 48-year-old musicians."