It was a contractual dispute that supposedly kept Black Sabbath drummer Bill Ward from joining his mates for their upcoming tour and album, but Ozzy Osbourne says there is another side to the story. The singer questions if Ward was physically up for touring and recording.

"You know them yellow f---ing stick-on memo notes?" Osbourne asks during a recent interview with British music mag Mojo (quotes via Blabbermouth). "He had them all over his f---ing drums. I was like, 'What the f--k's that for, Bill?' He said, 'I can't remember what I'm doing.'"

Osbourne adds, "I go, 'How are you gonna remember out of those 500,000 bits of paper stuck all over your kit, which one you're looking at, Bill?' (He said) 'I'll know.' Ah, OK great."

Rage Against the Machine drummer Brad Wilk plays drums on '13' -- available June 11 -- and Osbourne's touring drummer Tommy Clufetos drummed during the three Black Sabbath shows in 2012. Clufetos is currently on the road with Black Sabbath in Australia.

Troubles began before Ward bowed out of the reunion, during initial rehearsals. Osbourne says the band had serious concerns about whether he could hold up for two to three hours on stage. "My suggestion was that we run through a set and see how he got on because he was so out of condition and the drummer is the most demanding job in the whole band," he tells Mojo.

"We looked at Bill, and he couldn't remember what the f--- we were doing. But he didn't come clean and say, 'I can't cut this gig, but can we work something out, guys, where I'll come on but with another drummer backing me up?' Or, 'I'll come and play a few songs.' That would have been cool."

Ward announced he wasn't rejoining the band in May 2012, six months after a triumphant press conference that announced the group's reunion. Since then there have been a few sharp back-and-forth jabs between band mates, but all appear to be on mostly friendly terms at present. Osbourne's comments likely won't heal any existing wounds.

More From Ultimate Classic Rock