According to Jack Osbourne, Tony Iommi was the only person capable of challenging Ozzy Osbourne.

Jack was the latest guest on Billy Corgan's The Magnificent Others podcast, where he shared insights about the “interesting dynamic” between his father and Iommi — particularly an instance that occurred between the Black Sabbath bandmates prior to their final show last year.

“There was always an interesting dynamic between my dad and Tony, and [I’m] not revealing anything that people don’t know,” Jack said, later agreeing with Corgan’s suggestion that Iommi was like a “big brother” to Ozzy.

Jack shared how “nervous” Ozzy was about performing and ensuring it met everyone’s standards, especially during the massive “Back to the Beginning” concert last summer.

He elaborated that during Black Sabbath’s soundcheck, Iommi critiqued the way Ozzy sang.

“He was soundchecking, so he wasn’t going out there with his A-game on. He was just making sure everything worked and ran through the set,” Jack recalled. “Tony said, ‘Hey, you’re singing kind of flat.’

The comment upset Ozzy, according to Jack.

“My mom was like, ‘Oh you know dad…’ And I was like, ‘No I think it’s a good thing because out of the 40, whatever thousand people at that stadium, the only person that could ever say to my dad, ‘Hey, do better,’ was Tony and I think everyone needs someone like that,” Jack reasoned.

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He went on to compare his father’s relationship with his Sabbath bandmates to that of brothers, even if there were times of contention between them. Thus, he understood that Iommi made his remarks because they knew it was truly the last time they’d ever play live together again.

Jack told Corgan that Ozzy enjoyed watching his podcast and wanted to be a guest on it someday, which visibly flattered the Smashing Pumpkins frontman.

Watch the episode below.

Jack Osbourne Reveals the Only Person That Could Tell Ozzy to ‘Do Better’

See the favorite Black Sabbath albums of other rock and metal legends in the gallery below.