In his 2012 memoir, My Cross to Bear, Allman described how Duane was a central figure in his life in the years after their father was murdered by a man he met in a bar. The two boys endured a spell in a military school before being swept up in rock music in their teens. Although Gregg was the first to pick up a guitar, it was Duane who excelled at it.
So Gregg later switched to the organ.
They failed to crack success until they formed The Allman Brothers Band in 1969. Based in Macon, Georgia, the group featured Betts, drummers Jai Johanny "Jaimoe" Johanson and Butch Trucks and bassist Berry Oakley. They partied to excess while defining a sound that still excites millions.
Their self-titled debut album came out in 1969, but it was their seminal live album "At Fillmore East" in 1971 that catapulted the band to stardom.
Duane Allman had quickly ascended to the pantheon of guitar heroes, not just from his contributions to the Allman band, but from his session work with Aretha Franklin, Wilson Pickett and with Eric Clapton on the classic Layla and Other Assorted Love Songs album. But he was killed in a motorcycle accident in October 1971, just months after recording the Fillmore shows. Another motorcycle accident the following year claimed Oakley's life.
In a 2012 interview with The Associated Press, Gregg Allman said Duane remained on his mind every day. Once in a while, he could even feel his presence.
"I can tell when he's there, man," Allman said. "I'm not going to get all cosmic on you. But listen, he's there."
The 1970s brought more highly publicized turmoil: Allman was compelled to testify in a drug case against a former road manager for the band and his marriage to the actress and singer Cher was short-lived even by show business standards.
In 1975, Cher and Allman married three days after she divorced her husband and singing partner, Sonny Bono. Their marriage was tumultuous from the start; Cher requested a divorce just nine days after their Las Vegas wedding, although she dismissed the suit a month later.
Together they released a widely panned duets album under the name Allman and Woman. They had one child together, Elijah Blue, and Cher filed for legal separation in 1977.
The Allman Brothers Band likewise split up in the 1980s and then re-formed several times over the years. A changing cast of players has included Derek Trucks, nephew of original drummer Butch Trucks, as well as guitarist Warren Haynes.
Starting in 1990, more than 20 years after its founding, the reunited band began releasing new music and found a new audience. In 1995 the band was inducted into the Rock and Roll Hall of Fame and won a Grammy Award for best rock instrumental performance for "Jessica" the following year.
In 2000, Betts was ousted from the band via fax for alleged substance abuse and poor performance and he hasn't played with the band since.
Butch Trucks died in January 2017. Authorities said he shot himself in front of his wife at their Florida home.
In his memoir, Allman said he spent years overindulging in women, drugs and alcohol before getting sober in the mid-1990s. He said that after getting sober, he felt "brand new" at the age of 50.
"I never believed in God until this," he said in an interview with The Associated Press in 1998. "I asked him to bring me out of this or let me die before all the innings have been played. Now I have started taking on some spiritualism."
However, after all the years of unhealthy living he ended up with hepatitis C which severely damaged his liver. He underwent a liver transplant in 2010.
After the surgery, he turned music to help him recover and released his first solo album in 14 years Low Country Blues in 2011.
"I think it's because you're doing something you love," Allman said in a 2011 interview with The Associated Press. "I think it just creates a diversion from the pain itself. You've been swallowed up by something you love, you know, and you're just totally engulfed."
The band was honored with a lifetime achievement Grammy in 2012.