Why Knut the Polar Bear Died So Suddenly

He spawned millions of fuzzy toys, garnered media attention on everything from his cod-liver diet to his lack of mates and even inspired his own song before his untimely death in 2011. He was Knut the polar bear, the star of the Berlin Zoo. It turns out that Knut was killed by an autoimmune disorder called anti-NMDA receptor encephalitis, a kind of brain inflammation.