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.
Bear keeper Heiner Kloes said 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. Former reality TV star Paris Hilton was among Knut's many famous fans.
A post mortem will be conducted on Monday to try pinpoint his cause of death, bear keeper Kloes said.
Although Knut was the first polar bear to be born and survive at Berlin Zoo in more than 30 years, his young life was blighted by tragedy from the start.
Both he and his twin were rejected by their mother at birth and his brother died four days later.
But Knut amazed medical staff at the zoo by clinging to life. After spending his first 44 days in an incubator, he was put in the care of zoo keeper Thomas Dörflein, who began raising the infant with round-the clock care.
But tragedy struck again before Knut's second birthday in 2008, when Mr Dorflein died of a sudden heart attack at the age of 44.
Observers noted that the bear appeared to suffer from depression in the weeks after his beloved keeper and constant companion died.
Experts had earlier warned that the Knut was developing into a 'psychopath' who was too dependent on human contact.
Paris Hilton in Berlin
Champion Swimmer 北极熊连续游泳9天