Relive ABBA, Olivia Newton-John and Andy Gibb's incredible "jam session" from 1978

What happens when some of the world's biggest musicians come together for a "jam session"? You get pure magic ...

Sat in a circle, Olivia Newton-John and Andy Gibb joined ABBA on stage in 1978 to belt out a medley of ABBA hits, including 'Dancing Queen' and 'Fernando' - and their vocals together are truly spine-tingling.

But it was the performance that followed which was the really special musical moment ...

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The talented musicians faultlessly harmonised on songs from the Bee Gees, Elvis Presley and the Beach Boys, including 'Help Me, Rhonda' and 'Barbara Ann.'

As Olivia taps away on the drums, Benny Andersson can be seen playing the piano, while Björn Ulvaeus and Andy strum guitars and Anni-Frid Lyngstad shakes a tambourine.

Between moments of storytelling and conversation, the group slips in and out of music with ease.