Michael Jackson the "KING OF POP" is no more

Michael Jackson, defined in equal parts as the world's greatest entertainer and perhaps its most enigmatic figure, was about to attempt one of the greatest comebacks of all time. Then his life was cut shockingly — and so far, mysteriously — short.

The 50-year-old musical superstar died Thursday, just as he was preparing for what would be a series of 50 concerts starting July 13 at London's famed 02 arena. Jackson had been spending hours and hours toiling with a team of dancers for a performance he and his fans hoped would restore his tarnished legacy to its proper place in pop.

An autopsy was planned for Friday, though results were not likely to be final until toxicology tests could be completed, a process that could take several days and maybe weeks. However, if a cause can be determined by the autopsy, the results will be announced, said Los Angeles County Coroner Investigator Jerry McKibben.

Police said they were investigating, standard procedure in high-profile cases.

Jackson died at UCLA Medical Center after being stricken at his rented home in the posh Los Angeles neighborhood of Holmby Hills. Paramedics tried to resuscitate him at his home for nearly three-quarters of an hour, then rushed him to the hospital, where doctors continued to work on him.

"It is believed he suffered cardiac arrest in his home. However, the cause of his death is unknown until results of the autopsy are known," his brother Jermaine said.

Cardiac arrest is an abnormal heart rhythm that stops the heart from pumping blood to the body. It can occur after a heart attack or be caused by other heart problems.