Michael Jackson may have been more prince than king of pop, a French doctor says in a new book alleging his wide-ranging voice resulted from a childhood chemical castration to fight acne.

"When he died, I realised that he was an unusual phenomenon," Alain Branchereau, an opera buff and professor of vascular surgery at Timone University Hospital in France's Mediterranean port of Marseille, told AFP. "I said, 'That's the voice of a castrato!'."