Tony Iommi, Black Sabbath guitarist and co-founder, told UK broadcaster ITV that Osbourne was “frustrated” during the band’s farewell concert on July 5. The heavy metal icon died less than three weeks later, on July 22, at age 76.

Born John Michael Osbourne, the English musician rose to fame as the so-called Prince of Darkness with his heavy metal band, Black Sabbath, which he co-founded in 1968. The band released popular hits like “Paranoid,” “Iron Man” and “War Pigs.”