“It's the biggest show on the planet... I'm like, ‘Oh you gotta be kidding me right?’” Zakk Wylde recalls his “Spinal Tap moment” during Back to the Beginning

Musician/vocalist Zakk Wylde performs in concert at Emo's on July 10, 2016 in Austin, Texas.

Having Zakk Wylde for what would turn out to be Ozzy Osbourne's – and by extension, Black Sabbath's – final show, Back to the Beginning, was a no-brainer considering he was, on and off, the Prince of Darkness’ right-hand man and go-to guitarist since 1987.

However, such a large-scale event doesn't happen without its fair share of technical hurdles, and Wylde recalls what he calls his “Spinal Tap moment” during the show that drew 40,000 metalheads to Villa Park in Birmingham, and an additional 5.8 million on the accompanying livestream.