The American rock band confirmed the news on Twitter by posting, "It is with deep sadness we announce that Gregg Allman... Passed away peacefully at his home."
Another statement that was posted on Allman's website read, "Gregg struggled with many health issues over the past several years. During that time, Gregg considered being on the road playing music with his brothers and solo band for his beloved fans, essential medicine for his soul."
The cause of death was not immediately revealed, but the legendary singer was diagnosed with hepatitis C in 1999 and underwent a liver transplant in 2010.
Born in Nashville, Tennessee, Gregg, who co-founded the Allman brothers at the age of 22, fronted it for 45 years alongside his brother Duane Allman, who is considered as one of the most influential guitarist in the history of rock music.
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One of their early bands, The Escorts, evolved into the moderately successful Allman Joys in the mid-1960s. In 1969, they were signed - along with Oakley, guitarist Dickey Betts and drummers Jai Johanny "Jaimoe" Johanson and Butch Trucks - as The Allman Brothers Band by Macon, Ga-based Capricorn Records.
Shortly thereafter, Gregg recorded his debut studio solo album 'Laid Back' in 1973, which offered his varying influences, including rhythm and blues and soul music.
He married singer-actress Cher in 1975 and had a son Elijah Blue Allman, who is also a musician. She filed for divorce nine days after the wedding because of Gregg's heroin and liquor problems, reconciled within a month, and separated later.
Gregg's drug problem also led to the Allman Brothers' split after the recording of their unimpressive 1975 release 'Win, Lose or Draw'.
With his 1986 "I'm No Angel", Gregg enjoyed something of a comeback and also reunited with Allmans the same year. His other hits included "Midnight Rider", "Ramblin' Man", "Soulshine", "Whippin' Post" and "One Way Out".
He was inducted into the Rock and Roll Hall of Fame and the Georgia Music Hall of Fame in 1995 and also received a Lifetime Achievement Award at the 2012 Grammys.
Last year, Gregg was forced to cancel his summer tour due to unspecified "serious health problems."