Scientists in Germany say they have finally figured out what killed Knut, the polar bear who became a worldwide celebrity.

Knut drowned four years ago after swelling of his brain caused him to collapse and fall into his enclosure’s pool at Berlin Zoo.

In an article published by the journal Nature Scientific Reports, researchers say Knut suffered from anti-NMDA receptor encephalitis, an autoimmune disease discovered in humans eight years ago and never previously found in animals.

Alex Greenwood of the Leibniz Institute for Zoo and Wildlife Research says the discovery paves the way for treatment of other animals with the disease.

He said the case may also help raise awareness of what he called “Knut’s disease” and ensure early treatment for the one in 200,000 people affected every year.