British singer Elton John calls Michael Jackson "mentally ill" in his new book and said it was "disturbing" to be around him, BTA reported.

72-year-old John first meets the future King of Pop in the early days of his career. The Rocketman singer does not hide that over time he began to worry about Jacko's condition, who died in 2009 at the age of 50.

In an excerpt from her new autobiography, “Me,” Elton John writes,"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 goes on to say, "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."

Then comes the big allegation, with Elton writing ... "I don’t mean that in the light-hearted way. He was genuinely mentally ill, a disturbing person to be around."

Elton John also remembers a case where he invited Michael Jackson to a party. John claims that Jackson left the party and was found playing with the housekeeper's son.

"For whatever reason, he couldn’t seem to cope with adult company at all." John wrote.