You know the story: Brian Jones gets kicked out of the Stones, the Stones replace him with Mick Taylor and get ready to debut their new lineup at an outdoor concert in Hyde Park---which Jones dies two days before, turning the whole thing into a memorial show that 80,000 people showed up to attend.
From Wikipedia: "The Rolling Stones performed at a free concert in Hyde Park
on 5 July 1969, two days after Jones's death. The concert had been scheduled weeks earlier as an opportunity to present the new guitarist, and the band decided to dedicate the concert to Jones. Before the Rolling Stones' set, Jagger read excerpts from "Adonais
", a poem by Percy Shelley
about the death of his friend John Keats
, and stagehands released hundreds of white butterflies as part of the tribute. The band opened with a Johnny Winter
song that was one of Jones's favourites, 'I'm Yours and I'm Hers.'"