Black Sabbath keyboardist Geoff Nicholls has died at the age of 68
The former rocker lost his battle with lung cancer on Saturday, with his bandmate Ozzy Osbourne describing the keyboardist as "a great friend of mine."
Tweeting his upset, the frontman wrote: "Geoff Nicholls was a great friend of mine for a long time. He will be greatly missed. I'm very saddened at the news."
Tony Iommi also took to social media to express his sadness, lamenting on Facebook: "I'm so saddened to hear the loss of one of my dearest and closest friends Geoff Nicholls.
Geoff joined the group in 1979 before quitting in 1996, though made frequent returns until 2004
I will miss him dearly and he will live in my heart until we meet again.
"He's been suffering for a while now with lung cancer and he lost his battle this morning. Geoff and I have always been very close and he has been a real true friend to me and supported me all the way for nearly 40 years.
"I will miss him dearly and he will live in my heart until we meet again. Rest In Peace my dear friend. Tony."
Rounding off the tributes was bassist Geezer Butler, who wrote: "Very sad to hear of old friend and Sabbath keyboard player Geoff Nicholls passing. RIP Geoff (sic)."
Geoff made his Black Sabbath debut on the band's 1980 album Heaven and Hell after joining in 1979.
He left the band in 1996 but made occasional returns until 2004, when keyboardist Adam Wakeman, a member of Ozzy's touring band, was hired as his replacement.
Black Sabbath members (from left) Geezer Butler, Tony Iommi and Ozzy Osbourne have all paid tribute
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The heartbreaking news comes after Tony was diagnosed with lymphoma cancer in 2013, with the musician previously claiming that his treatment unintentionally prompted the departure of Bill Ward.
"My illness has changed my life a lot and my attitude," he said while recording the band's LP 13 the same year as his diagnosis. "When I was going through my treatment, I didn't think I was going to last, I had stage three lymphoma.
"I wanted to get things going quick, and Bill wanted to take longer. Bill seemed to feel he was getting a bad deal. We never dealt with that, we left all that to management."
He added: "We just wanted to play together and enjoy it. We were playing with Bill for a bit and then he never turned up. I thought, 'What's going on?"