As rock stars competed to express the depth of their feelings for the plight of Africa last weekend, one musician who seemed genuinely choked to be on stage at Live 8 never mentioned Africa at all.

Roger Waters, the 60-year-old bass player with Pink Floyd, had reconvened their “classic” formation for the first time in nearly a quarter of a century.

When, midway through their 20-minute set, Waters announced he felt “incredibly emotional to be back with these three guys again”, he wasn’t being showbiz: he meant it. As he tried to sing Wish You Were Here, a song about Syd Barrett, his childhood friend and the band’s inspirational founder who left in 1968, his voice cracked and he could barely get the words out.

David Gilmour — Waters’s arch-rival in one of the longest feuds the rock world has ever witnessed — carried on scowling down at his electric guitar. Although the band played on, none of them had expected such a public declaration from the man who had sued, insulted and mostly just ignored them for the past 20-odd years. Even Nick Mason, the group’s unflappably urbane drummer — and the only member on speaking terms with Waters before the Live 8 reunion — admitted later that “we were all very surprised at the way Roger behaved”.

Almost as surprised as they had been back in 1986 when Waters launched a legal action in the High Court to stop his old partners from carrying on as Pink Floyd. This was the first time a band’s name was fought over as if it were a brand name. Waters had quit the group to launch a solo career in 1985. His view was that since he had written most of the music after their breakthrough album, the 35m-selling Dark Side of the Moon in 1973, without him at the helm Pink Floyd did not exist.

Mason and more particularly Gilmour — a virtuoso guitarist, singer and songwriter of a handful of Pink Floyd’s best-loved tunes, including Comfortably Numb — saw this as breathtaking arrogance on Waters’s part, the culmination of years of bossiness verging on megalomania from the group’s self-appointed leader.

A year later they had fought him and won. What followed were two further Pink Floyd albums — led by Gilmour and supported by a couple of hugely profitable world tours — and a lot of backbiting. Gilmour’s most-quoted comment on Waters was the pithy “Roger is a prick.”

Waters, meanwhile, heaped scorn on Gilmour’s musical talent and his reliance on others to help with the songwriting, including his wife, the novelist Polly Samson. “So Spinal Tap,” Waters bitched. Before they met to rehearse four songs for Live 8, the two men had scarcely spoken for 20 years.

The origins of their feud actually went back another 30. Most accounts of the beginnings of Pink Floyd start at Regent Street Polytechnic, London, in 1964, where three architecture students, Roger Waters, Nick Mason and Rick Wright, joined forces with a student from Camberwell art school, “Syd” — real name, Roger — Barrett.

The real foundations of the band, though, had been laid much earlier in Cambridge where Barrett, Waters and a young sidekick, David Gilmour, had grown up together. Their mothers all had connections with Homerton, the nearby teachers’ training college. Waters and Barrett shared the same primary and grammar schools and were drawn together in part because each had lost his father.

Gilmour and Barrett became friendly in their teens and ended up at Cambridge technical college studying for A-levels. In the summer of 1964 the pair went busking in St Tropez, playing Beatles songs on the streets before getting thrown in jail by French police.

Four years later they were playing together again in far less happy circumstances. Barrett — by now the charismatic leader and songwriting dynamo of the darlings of the British underground scene, Pink Floyd — had taken too much LSD and become an “acid casualty”. Gilmour had been drafted in, initially to hold things together, then, as Barrett’s madness took hold, as a full-time replacement.

Peter Jenner, the band’s first manager, recalled that Waters “was the one who had the courage to drive Syd out, because it was chaos”, but that it hurt. “Syd was the only person, I think, who Roger has ever really liked and looked up to, and he always felt very guilty about the fact that he’d blown out his mate.”