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.

"I didn’t realize then that I would never see Ozzy again after that night," Butler writes of the July 5 "Back to the Beginning" show in England.

The all-star 'Back to the Beginning' concert made more than $200 million, the highest-grossing charity concert since the Concert for Bangladesh.