After beating the odds as the only polar bear ever raised by humans, Knut the polar bear cub was found dead at the Berlin Zoo on Saturday.
According to reports, the beloved four-year-old cub was found alone, floating in the water in the zoo's polar bear enclosure. Bear keeper Heiner Kloes was quoted as saying, "He was by himself in his compound, he was in the water, and then he was dead ... He was not sick, we don't know why he died."
More than 600 people were looking on as the bear collapsed. The cause of death has not been determined. An autopsy is expected to be performed on Monday.
Knut was raised by zookeepers after he was rejected by his mother shortly after birth in 2007.
See more photos of Knut the polar bear below.