The song, written by Derek Trucks and Doyle Bramhall II, was previously only available as a special edition 12-inch disc as part of Record Store Day.
As 'Brothers and Sisters' entered the album chart, its Dickey Betts song ‘Ramblin’ Man'' hit the Hot 100 to become the band's first major hit.
Allman's solo debut, 'Laid Back' peaked at number 13 on the Billboard chart while its signature hit ‘Midnight Rider’ became a top 20 hit across North America.
The late, lamented guitarist also played the guitar on the Allman Brothers Band's first two albums.
The song had both historical significance and huge poignancy in the pre-ABB days of Duane and Gregg Allman.
From powerhouse belters to multi-octave vocalists with mind-boggling versatility, the best male rock singers have left their mark on music history.
History has tended to overlook the festival that was bigger than Woodstock, Monterey or the Isle of Wight.
The esteemed Southern rock act performed at Ramblin' Man in support of their recent album, 'Down To The River'.
'At Fillmore East' cemented the band's live reputation for delivering incendiary southern rock.
In the grounds of a stately home in Hertfordshire, the Bucolic Frolic culminated in some mighty southern rock.
'Laid Back' first appeared in October 1973 and is vastly expanded for this release, while the live set has been unavailable for more than 30 years.
The great writer-guitarist, with wife Bonnie, made some of the best blues, rock and gospel-flavoured US music of their generation.
The titles include the band's self-titled debut from 1970, 'Eat A Peach' and the much-acclaimed live album, 'At Fillmore East'.
Gregg was born on 8 December 1947 in Nashville, one year the junior of brother Duane, with whom he would co-found the mighty blues-rock institution the Allman Brothers Band.
They will be joined on the Prog In The Park stage by Polish outfit Riverside and Pain Of Salvation, with further artists to be announced.