He stole drugs from guitarist Duane then lied about it the morning before his older sibling died in a motorbike crash in 1971, aged 24.
And in his book My Cross to Bear, the musician admits he’ll never forgive himself.
Allman explains he’d given Duane $100 to buy him a gram of coke, but the drug didn’t arrive. In retaliation he went to his brother’s house the next day, let himself in and located his stash. The singer “poured out about half a gram and snorted it up.”
When he got home an angry Duane called him and accused him of stealing. He writes: “That last thing I ever said to my brother was a fucking lie, man: ‘No, I did not,’ I told him.”
The guitarist apologised for making the accusation and said: “I sure do love ya, baybrah.” Allman continues: “That was the last time I ever spoke to my brother.
“I have thought of that lie every day of my life, and I just keep recrucifying myself for it. I know that’s not what he would want – well, not for long anyway. I know he lied to me about the blow in the first place.
“But the thing is, I never got the chance to tell him the truth.”
Allman is honest about his relationship with his bandmates and his lifestyle in the book, explaining he was “shit-faced drunk” during the band’s Rock And Roll Hall of Fame induction and doesn’t remember a moment of it. He’s survived a number of health episodes related to his drink and drugs intake – most recently he had to postpone his book tour because he needed urgent heart checks.
But looking back on his career he reflects: “A player has got to play. If travelling and making music is what takes me, I can’t think of a better way to go.”