The 61-year-old former member of powerhouse trio the Jimi Hendrix Experience was found dead in a hotel room in the United States yesterday.
Authorities said he appeared to have died from natural causes.
Mitchell, from Ealing in west London, secured his place in rock history after joining legendary guitarist Jimi Hendrix and bass player Noel Redding in 1966.
Mitchell also played with a host of other rock legends, including Eric Clapton, John Lennon, the Rolling Stones, Jack Bruce, Jeff Beck and Muddy Waters.
Hendrix's stepsister, Janie Hendrix, said of the drummer: "He was a wonderful man, a brilliant musician and a true friend."