Instead he insists the band had already made a decision to abandon the thrash musical ethic, and he just helped them go where they wanted to go by persuading them to follow drummer Lars Ulrich more than they'd done in the past. And he admits the experience was so fraught he told the band he'd never work with them again – and he believed the feeling was mutual.

Marking the twentieth anniversary of Metallica's self-titled release, known as the Black Album by most fans, Rock tells MusicRadar: "They had broken through to one level but they still weren't on mainstream radio. When they came to me they were ready to make that leap to the big, big leagues.