Washington, June 29 Michael Jackson's son was with the singer when he collapsed, and thought his father was just "clowning around", according to a family friend.

Jackson biographer Stacy Brown alleged 'Prince' Michael Jackson Jr. witnessed his father hit the ground in the living room of their rented California home.

The author claimed the 12-year-old stood as a silent spectator, while his father's doctor Conrad Murray made frantic attempts to save the King of Pop.

"The horror of it all is that Prince thought this dad was just being his dad and clowning, but it was real and he watched as they worked on him," Contactmusic quoted him as having told the New York Post.

"Prince was stunned - in a trance - just watching," he added.

The thriller was pronounced dead three hours later at Los Angeles's UCLA Medical Center.

He is believed to have suffered an apparent cardiac arrest, but medical examiners are yet to determine the cause of his death. (ANI)