Tony Iommi is "worried" about the "unknown" at Black Sabbath's last-ever show this summer.

The Paranoid hitmakers are to bow out with a farewell gig at Birmingham's Villa Park, where the likes of Metallica, Slayer, Pantera, Gojira, Halestorm, Alice In Chains, and Lamb of God will also perform on July 5th.

Tony admitted there are "so many other moving parts" to the upcoming spectacle, and he is also unsure whether Sabbath frontman Ozzy Osbourne will be "standing or sitting on a throne" when he performs with the group.

He told Music Week: "This would be a big, monumental thing if it all comes good. The worrying thing for me is the unknown.

"We don't know what's going to happen. Normally, when we'd tour, we'd rehearse and run through the thing for a while, and it's just us. But with this event there are so many other moving parts.

"You're used to Ozzy running around, but he certainly won't be doing that for this show. I don't know if he's going to be standing or sitting on a throne or what."

In February, Ozzy - who has neck and spinal issues, as well as Parkinson's disease - insisted he isn't planning to do a full set with Sabbath, but reassured fans he is hoping to do "little bits and pieces" at their farewell show.

Ozzy - who hasn't played a full show for six years - said on his SiriusXM show Ozzy Speaks: "I'm not planning on doing a set with Black Sabbath but I am doing little bits and pieces with them. I am doing what I can, where I feel comfortable."

Speaking in February, he said: "I am trying to get back on my feet... When you get up in the morning, you just jump out of bed. I have to balance myself, but I'm not dead. I'm still actively doing things."

Ozzy's wife Sharon Osbourne previously told how he was "overwhelmed" by the number of stars who want to be involved with the show.

Speaking to Birmingham Live, she said: "I think it's the best metal gig ever. It's easy when you have such good friends and friends that support you. We've known these guys for years and years and many of them were passed the torch by Sabbath.

"It goes down the line. When you need them, they come ... He's overwhelmed. He's very overwhelmed by the response of his friends. He said 'wow, they're doing this for me?'

"When you've got your peers, and your friends with you, there's nothing bigger. Well, aside from fans, of course. They come first."