An excerpt from the late Ronnie James Dio’s memoir reveals that he’d “shied away” from joining Black Sabbath when he was first asked.

Rainbow in the Dark: The Autobiography, which was completed by journalist Mick Wall and Dio’s wife Wendy, will be published on July 27. In a passage released via Rolling Stone, the singer told of the reason he overcame his doubts and decided to replace Ozzy Osbourne in 1979.

At the time, he’d recently left Rainbow, and a chance encounter with Tony Iommi had led to the pair writing songs together. At first both were considering a project separate from Sabbath, but the “next logical step” was to invite him to become a member of the British icons.

“I admit, at first, I shied away from the prospect,” Dio wrote. “I was desperate to do my own thing again after the years working under Ritchie Blackmore’s rule. I was also unsure how on earth I was supposed to replace Ozzy Osbourne in Black Sabbath. Unlike in years to come, when groups like Van Halen, Bad Company, Iron Maiden, and even Queen could bring in a new frontman with impunity, in the late '70s, the idea of a superstar group like Sabbath replacing their frontman was considered unthinkable. Led Zeppelin without Robert Plant, the Rolling Stones without Mick Jagger? Sacrilege."

He added that already having a profile in the rock world could have been a “double-edged sword” because he could “end up alienating both Sabbath and Rainbow fans.” But Iommi insisted he could do it, and the guitarist’s certainty led to a split with infamous manager Don Arden. “He canceled the lease on the house he was renting for [Sabbath] and sold their management contract to a guy named Sandy Pearlman," Dio said. "He then told [daughter] Sharon to start taking care of Ozzy as a solo artist: the beginning of a long and incessantly winding road that deserves a book of its own.”

Dio explained that he felt better about the idea after Iommi promised he’d be an equal partner in the band, rather than the situation in Rainbow where “Ritchie was the boss and that was that.” He continued: “The real clincher though was when Wendy got hold of me and told me straight: ‘Ronnie, we’ve got less than eight hundred bucks in the bank, we’ve got to do something!’ … I phoned Tony: ‘Okay, man, I’m in. When do we start?’”

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