U2's longtime tour manager died Wednesday in Los Angeles, where the Irish rockers are playing a series of concerts, the band said.
Dennis Sheehan, who was in his late 60s, was pronounced dead in his hotel in West Hollywood, where paramedics were called around 5:30 am to treat a person for a reported cardiac arrest, TMZ said.
"We've lost a family member, we're still taking it in," said U2 frontman Bono in a statement issued by the band's publicist.
"He wasn't just a legend in the music business, he was a legend in our band. He is irreplaceable."
Arthur Fogel, head of the band's touring management company, added: "With profound sadness we confirm that (Sheehan) has passed away overnight.
"Our heartfelt sympathy is with his wonderful family," he said, calling Sheehan "a dear friend to us all."
Sheehan had worked for U2 for more than 30 years, and had also worked with other rock legends including Led Zeppelin, Iggy Pop, Patti Smith and Lou Reed, TMZ reported.
On Tuesday the Irish band played the first of five scheduled concerts in Los Angeles. Their "Innocence and Experience" tour began earlier this month in Vancouver, where guitarist the Edge fell off the stage during the first show.