From People

Jackson was pronounced dead at 2:26 p.m. at the Ronald Reagan UCLA Medical Center not far from his rental mansion in the Holmby Hills. The cause of death wasn't known. An autopsy is set for Friday.

"It's a very sad day for all of us," Jackson's manager, Frank DiLeo, tells PEOPLE. " It's such a terrible shame. He was my friend." As for Jackson's three children – Blanket, 7, Paris, 11, and Prince Michael, 12 – DiLeo says, "The kids are very upset, but they are fine."

The entertainer was stricken Thursday afternoon and a 911 call was placed. "His personal physician, who was with him at the time, attempted to resuscitate Jackson, as did paramedics who transferred him," according to a statement from the hospital.