Heaven & Hell bassist Geezer Butler has mixed feelings about the band's July 24 performance at the High Voltage Festival. On the one hand, he looked forward to paying a proper tribute to band's late vocalist Ronnie James Dio, who died from stomach cancer on May 16. However, he's aware that performing the songs while other vocalists are behind the microphone re-emphasizes the singer's absence.

"I think it will be exciting and a bit sad at the same time," Butler told Noisecreep. "He was a one-off great person -- utterly irreplaceable. He was a great guy to know, a great friend to me and it was just fantastic working with him."

For the High Voltage Festival concert in London's Victoria Park, Heaven & Hell were joined by ex-Black Sabbath vocalist Glenn Hughes (ex-Deep Purple) and Masterplan vocalist Jorn Lande, who released released a tribute to Dio, which features songs by Rainbow, Dio and Black Sabbath.

Before Dio became critically ill with stomach cancer, Heaven & Hell had booked shows in Europe with Metallica throughout August. "Six weeks before we were supposed to start rehearsals, Ronnie got really, really bad and we had to cancel the tour," Butler said. "The medical treatment seemed to be working and we all thought he was getting better. It was totally unexpected [when his health failed]."

After Dio died on May 16, the band's European promoter suggested Heaven & Hell play the High Voltage festival show as a tribute to their fallen frontman. "He's going to donate all the money to Ronnie's cancer fund, [Stand Up and Shout]," Butler said. "So we said, "Yeah, as long as all the money goes to Ronnie's charity we'll do it."

Butler performed on and off with Dio since the 1980 Black Sabbath comeback album 'Heaven and Hell,' the group's first recording after Ozzy Osbourne was fired from the band. While Sabbath's career with Dio started and ended with a band, the singer and his bandmates also experienced some major turbulence. While 1980's 'Heaven and Hell' album was a big success, tensions developed during the making of the follow-up, 1981's 'Mob Rules,' and after the December 1982 release of the concert album 'Live Evil,' Dio left Black Sabbath and formed his own band, Dio.

He returned to Black Sabbath a decade later to write and record the 1992 album 'Dehumanizer,' but at the end of a tour for the record, Black Sabbath agreed to open for Ozzy Osbourne in Costa Mesa, Calif. during what they thought would be Osbourne's farewell tour, and have Ozzy join Black Sabbath on stage. Dio, who strongly disapproved of the idea, quit the band and returned to his solo career.

Then, in 2006, Rhino Records asked Butler, Dio and Iommi if there were any outtakes they could use for a compilation album 'Black Sabbath: The Dio Years.' Since there was nothing in storage, the members decided to get back together to write three new songs on the album. The sessions went so well that the members decided to tour as Heaven & Hell and play material from their three albums along with the new songs.

They released the live CD and DVD 'Live From Radio City' in 2007, then toured with Judas Priest, Motörhead and Testament on the Metal Masters Tour. Other tours followed before the members of Heaven & Hell decided to return to the studio and record their third full album together, 'The Devil You Know,' which came out in 2009. The album and the tour that followed were tremendously successful, which, in retrospect, provided closure to the band, which went out on one of Dio's legendary high notes.

"It was almost as if fate had a hand in it," Butler told Noisecreep. He sniffed and paused to recompose himself then concluded, "Well, he's at peace now, anyway."

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