Michael Jackson's eldest son thought his father was joking around when he collapsed on the living-room floor — but soon stood "in a trance" as the King of Pop's personal doctor frantically tried to revive him, a family confidant told the New York Post.

"The horror of it all is that Prince thought his dad was just being his dad and clowning, but it was real, and he watched as they worked on him," said Stacy Brown, a Jackson family biographer who has spoken extensively to the Jackson's relatives since he died Thursday.

"Prince was stunned — in a trance — just watching," Brown said. "There was no movement, just looking around and not really processing what was really happening."

Brown said he was told that when Jackson went into cardiac arrest, he was in the living room of the $100,000-per-month Los Angeles rental with the 12-year-old boy — whose full name is "Prince" Michael Joseph Jackson Jr.

Also there were the pop star's personal physician, Dr. Conrad Murray, his longtime friend and one-time manager, Frank DiLeo, and a security guard named Tippy.

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