It is believed the pop icon died from heart failure.
George Michael's Wham! co-star said he is "cleft with grief" following the pop icon's death at just 53.
The British musician is believed to have died from heart failure in his home in Oxfordshire, England on Sunday.
After the news broke, fellow musicians took to social media to express their shock and heartbreak. Among them was Ridgeley, who performed alongside Michael in Wham! in the 1980s.
"Heartbroken at the loss of my beloved friend Yog," he wrote on Twitter Sunday. "Me, his loved ones, his friends, the world of music, the world at large. 4ever loved. A xx"
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Ridgeley later shared a quote from Michael that read: "I still believe that music is one of the greatest gifts that God gave to man." Ridgeley added: "God didn't give it, you did my old friend. Cleft with grief."
Other stars paid tribute to the prolific musician, including Elton John, who wrote on Instagram: "I am in deep shock. I have lost a beloved friend - the kindest, most generous soul and a brilliant artist."
James Corden, whose popular Carpool Karaoke segment began with Michael in 2011, said: "I've loved George Michael for as long as I can remember. He was an absolute inspiration. Always ahead of his time."
"He was so loved and I hope he knew it because the sadness today is beyond words," Boy George wrote. "Devastating. What a beautiful voice he had and his music will live on as a testament to his talent. I can't believe he is gone. I hope the Buddha will hold him in his arms."
Michael sold more than 100 million albums during a career that spanned nearly four decades.
He first saw success with Wham!, releasing beloved hits including "Wake Me Up Before You Go-Go" and "Last Christmas." In 1987, he released a solo album, "Faith," which went on to win a Grammy for album of the year. His hits included "Careless Whisper" and "Father Figure."
He released his last album, Symphonica, in 2014.
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On Sunday, Michael's family released a statement through his publicist saying he had passed.
"It is with great sadness that we can confirm our beloved son, brother and friend George passed away peacefully at home over the Christmas period," it said. "The family would ask that their privacy be respected at this difficult and emotional time. There will be no further comment at this stage."
Michael's manager Michael Lippman told Billboard that his cause of death was believed to be heart failure. He said the star was found in his bed.
Police said nothing about his death appeared to be suspicious.
"Thames Valley Police were called to a property in Goring-on-Thames shortly before 2 p.m. Christmas Day," he said. "Sadly, a 53-year-old man was confirmed deceased at the scene. At this stage the death is being treated as unexplained but not suspicious."
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