A friend of a friend*, unfortunately I never got to meet him.
*(My friend "Deacon" Jones who was the leader of John Lee Hooker's band for 15 yrs.) Allman played on a couple of Deacon's albums over the years. Deacon's wife told me that on their second date, Deacon took her to see Gregg Allman play, and Gregg, between songs, took to the mic and said that there was another organist who could do the song he was about to play justice and then called Deacon out of the audience to come play with the band. His wife only kind of knew about him being a musician, but had no idea until Allman did that.
You've probably never heard this, Allman with vocals.