BLACK SABBATH guitarist Tony Iommi has told Metal Hammer magazine that the band's headlining appearance at the Barclaycard British Summer Time festival at London's Hyde Park may turn out to be the legendary heavy metal group's final gig.The July 4 event will see SABBATH perform alongside SOUNDGARDEN, FAITH NO MORE, MOTÖRHEAD and SOULFLY on the festival's main stage. "It could be the last ever SABBATH show," Iommi told Metal Hammer. "I don't want it to be, but there's nothing really planned touring-wise after that show, so for all we know that could be it, really. To be honest, I don't want to be touring to this extent too much longer, because it makes me feel so bad." Iommi has had to go back to England every six weeks for treatment ever since being diagnosed with lymphoma in 2012, forcing him and SABBATH to work around both the treatments and the recovery time needed afterward. "I'm at a stage now where I have no support, which means I have to see whether the cancer is coming back or if it's still there or what," he said. "I just don't know. It's a bit of a worry. After we finish this tour, I'll go in and have scan, so we'll see what that shows up." "But the show at Hyde Park will a great way to end the European tour," he added. "It has a really great bill, with a really good mix of people. We haven't made any specific plans as the gig is a way off yet, but I think it'll be special." Last year, Iommi said that his ongoing treatments and their physical side effects could severely restrict SABBATH's activities, explaining, "I can't commit to doing another two years or anything like that. I have to play it as it comes now." Singer Ozzy Osbourne told The Pulse Of Radio that Iommi never let his treatments slow him down during the making of the recent SABBATH album, "13". "My hat goes off to him 'cause he really is Iron Man," he said. "I mean, that chemotherapy knocks you sideways, you know. I mean, when my wife had cancer a few years back, she was having three chemo things a month and it would knock the life out of — literally every time she'd have a treatment, she'd have a seizure. It's scary stuff. But he came down, plugged in and carried on. He's my hero, I swear to God he is." "13", the first SABBATH release in 35 years to feature Iommi, Osbourne and Geezer Butler playing together, was released in June 2013 and landed the band its first-ever No. 1 album in the U.S., also topping the chart in the U.K. and a number of other countries. The band also earned three 2014 Grammy Award nominations, for "Best Rock Album" for "13", plus "Best Metal Performance" and "Best Rock Song" for "God Is Dead?" The making of "13" was marked by several dramatic events, including drummer Bill Ward's withdrawal from the project over a contractual dispute. Butler told Revolver that he started writing a song for "13", called "Hanging By A Thread", that was inspired by Iommi's illness. He explained, "It was very much about dying, about giving your last breath and passing your spirit on." But the track didn't make it onto the album because, Butler said, "We never came up with the finished thing." SABBATH completed a 10-date North American run on April 26 in Los Angeles.