Sir Elton John has called Michael Jackson “mentally ill, a disturbing person to be around” in his memoir.

The superstar’s autobiography Me: Elton John has been packed with shocking revelations from his life in showbusiness, and in one section he details his experiences of spending time with the disgraced late star.

Jackson was the subject of a damning documentary, Leaving Neverland: Michael Jackson and Me, in which James Safechuck and Wade Robson spoke candidly about being children invited to the singer’s ranch at the height of his fame and accused him of years of abuse.

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Sir Elton said that when Jackson had been a child star himself, he had been very sweet, but then related how he felt that things had reached a turning point as he grew older.

He said: "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."

View photos Michael Jackson pays his respects to the late James Brown. (Rick Diamond/WireImage) More

It seemed that the Rocketman star had noticed something amiss about Jackson’s behaviour and speculated that it may have been affected by prescription drugs.

He said: "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.

"I don’t mean that in the lighthearted way. He was genuinely mentally ill, a disturbing person to be around."

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Jackson was known for his unusual close friendships with a number of children when he was an adult, most famously including the then-child star Macaulay Culkin.

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Sir Elton said: "For whatever reason, he couldn't seem to cope with adult company at all."

The memoir has included a number of other headline-worthy anecdotes, including throwing a dinner party where he says Sylvester Stallone and Richard Gere almost came to blows over Princess Diana, sharing a joke with the Queen, his row with Tina Turner, and his difficult relationship with his mother, saying he’s glad she never met his children.