Sir Elton John says Michael Jackson was "mentally ill" and "disturbing to be around".
The Rocketman singer - who first met the late King of Pop early on in his career - has claimed he became concerned about the Billy Jean hitmaker over the years.
In an excerpt from his new memoir Me, he wrote: "I'd known Michael since he was 13 or 14 ... He was just the most adorable kid you could imagine.
"But at some point in the intervening years, he started sequestering himself away from the world, and away from reality the way Elvis Presley did."
He alleged: "God knows what was going on in his head, and God knows what prescription drugs he was being pumped full of, but every time I saw him in his later years I came away thinking the poor guy had totally lost his marbles.