BERLIN – Berlin’s beloved polar bear Knut, an international star who as a cuddly, fluffy cub graced magazine covers, movies and merchandise, died Saturday. His death at the young age of 4 took zookeepers and animal experts by surprise.

The celebrity bear died suddenly in his compound at the Berlin Zoo on Saturday afternoon, bear keeper Heiner Kloes told The Associated Press. He waded into the water in his enclosure before having a short spasm and then dying in front of hundreds of zoo visitors.

Additional Photos

Knut, the now-famous polar bear cub, gives his first public appearance at the Berlin Zoo in 2007. An autopsy will be performed Monday to pinpoint the cause of death, which took zookeepers by surprise. 2007 Associated Press file

While the life expectancy of polar bear in the wild is between 15 and 20 years, animals in captivity can live even longer because they are not exposed to hunger, thirst or infections. An autopsy will be performed Monday to try to pinpoint the cause of death, Kloes said.

“He certainly did not die of old age,” Thomas Pietsch from the Vier Pfoten group for the prevention of cruelty to animals told German news agency DAPD.

His death was met by an immediate outpouring of sorrow. As the news of Knut’s death spread through the city, more Knut fans showed up at the zoo, assembling in front of the bear compound to mourn his loss.

Berlin Mayor Klaus Wowereit called Knut’s death “awful,” telling the B.Z. daily, “we all held him so dear.”

“He was the star of the Berlin zoos,” he said.

Rejected by his mother at birth on Dec. 5, 2006, along with his twin brother, who only survived a couple of days, Knut first attracted attention when his main caregiver, Thomas Doerflein, camped out at the zoo to give the button-eyed cub his bottle every two hours. Doerflein cuddled and played with him at daily public appearances to the delight of thousands of people who came to watch.

Fan clubs sprung up across the globe, including in Japan, the U.S. and Germany. Fans followed his every move, including his weight battle — he had a weakness for croissants — or plans to move to a different zoo.

“Knutmania” led to a 2007 Vanity Fair cover with actor Leonardo DiCaprio shot by photographer Annie Leibovitz, a film and plush likenesses. Though the zoo has never released exact numbers, Knut merchandise has brought in hundreds of thousands of euros.

He was so adored, and profitable, Berlin’s zoo paid some $600,000 to the Neumuenster zoo to settle a financial dispute over his ownership. Neumuenster owns Knut’s father and had insisted it was the legal owner of Knut, the elder bear’s first offspring.

No longer a cub, Knut grew rapidly, weighing a hulking 440 pounds by age 2, and trading in white fluff for yellowish fur. Doerflein, the zookeeper who raised him, died in 2008 of a heart attack, earning front page headlines in German newspapaper as “Knut’s daddy.”

Between 600 and 700 people were at his compound when Knut died, zoo officials said.

Some said they feared Knut had died from all the stress that stardom brings.

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