Knut the polar bear, who shared a Vanity Fair cover with Leonardo DiCaprio, has died.

The world-famous polar bear, who made headlines when he was hand-raised by zoo keepers after being rejected by his mother at birth in December 2006, died in his compound at a Berlin zoo today.

Bear keeper Heiner Kloes told the Associated Press that Knut "was by himself in his compound, he was in the water, and then he was dead." Kloes added, "He was not sick, we don't know why he died."

Between 600 and 700 people were at Knut's compound and saw the four-year-old bear die, German news agency DAPD reported.

Knut's popularity landed him on a 2007 Vanity Fair cover with actor DiCaprio shot by celebrity photographer Annie Leibovitz. Heiress and former reality TV star Paris Hilton was among Knut's many famous fans.

A post mortem will be conducted on Monday to try to pinpoint his cause of death, bear keeper Kloes said, according to AP.