Incredibly sad news from the Berlin Zoo today: Knut, the world famous polar bear, has died. A bear keeper at the zoo, Heiner Kloes told the AP:

"He was by himself in his compound, he was in the water, and then he was dead," said Kloes. "He was not sick, we don't know why he died."

An autopsy will be performed to determine the cause of Knut's death. He was 4 years old.

RIP, Knut.

[Image via AP]