A new BBC Radio 4 documentary claims the Hells Angels planned to kill Mick Jagger due to disputes that arose after the motorcycle gang--hired to perform security--killed an audience member during the Rolling Stones' disastrous Altamont show in 1969.
"They were gong to kill him for retribution for firing them," former FBI agent Mark Young told the documentary.
The group that set out to kill the singer were thwarted when their boat almost sank, he added, and they "never went back and reinstituted the plan".
The programme will be broadcast on 11 March at 1545 GMT.
You also should be able to visit the BBC's audio-on-demand site after that date to hear the show.