updated 03/19/2011 AT 2:45 PM ET
•originally published 03/19/2011 AT 1:30 PM ET
With a blue sky and the scent of spring in the air, Saturday afternoon in Berlin was the perfect time to visit the city’s zoo, but for some 600 visitors it turned into a horror: Before their eyes, Knut the polar bear collapsed, then floated dead in the water of his pen.
“It was a completely normal day: He was with the female bears before, who had just been shut away. Then, Knut strolled around the enclosure, went into the water, had a short spasm and died,” Berlin Zoo bear keeper Heiner Kloes told the Associated Press. An autopsy will be performed on the 4-year-old mammal to determine the cause of death. Polar bears in captivity have been known to live more than 30 years.
The city is in shock. Berlin Mayor Klaus Wowereit told the tabloid B.Z., “This is sad news. We were all so fond of him.”
Knut became a worldwide sensation soon after he greeted the world Dec. 5, 2006, as one of twins. His mother, Tosca, had rejected both bears, and his sibling died four days later.
The little polar bear thrived when caretaker Thomas Doerflein moved into the zoo and hand-raised him. Within a few months, Knut had an instant community of fans all around the globe thanks to his black-button eyes and sweet expression, much like a stuffed animal come to life. Those cute features inspired a line of toys, puzzles, posters, T-shirts, cell-phone ringtones and even a Vanity Fair cover shoot shared with Leonardo DiCaprio.
Yet, sadness and controversy followed Knut as he grew up before the public eye. In 2008, Doerflein died suddenly of a heart attack. A year later, the Berlin Zoo settled a custody battle over Knut with the Neumunster Zoo, where the polar bear’s father Lars resides, for $600,000.
Then came the smack heard ‘round the world: On Knut’s “first date” with girl polar bear Gianna, he got a little too close to his new mate (on loan from the Munich Zoo) and she let him know with a firm swat. As zookeeper Kloes said at the time, “It was as we expected it to be. Knut was very shy and the Munich bear was clearly the one wearing the dirndl.”
There was hope that the two would breed, and the polar bears seemed to have grown close, but Gianna was eventually sent back to Munich.
At the zoo Saturday, “everybody was asking, ‘What’s going on, why is Knut not moving?’” Camilla Verde, a 30-year-old Italian who lives in Berlin, told the AP. “All the zoo keepers who put up the fences were so very sad. One of them said, ‘He was our baby.’”
Read more about Knut on PEOPLEPets.com:
Knut’s 4th Birthday Celebration
PHOTOS: Gianna and Knut, a Love Story