Two weeks ago, the Berlin Zoo's most famous resident -- Knut, a 4-year-old polar bear -- was observed seizing up before collapsing into the water in front of a 600-person crowd. He died shortly after, much to the dismay of zookeepers and officials.

Since his March 19 passing, pathologists have studied Knut's body to determine the actual cause of death. They say he ultimately died from drowning, but that a serious underlying infection that caused his brain to swell was the true culprit.

Pathologists still aren't sure what cause the infection, but believe it was likely a virus that Knut carried for an extended period of time. Ongoing investigation into the death of Knut continues as fans around the world mourn.