Scientists have at last cracked the mystery surrounding the death of Knut, the much-loved polar bear who lived at Berlin Zoo.
The arctic mammal, who attracted millions of visitors to his exhibit, died suddenly after a seizure in 2011, collapsing into his enclosure's moat.
The cause of his downfall was a mystery to scientists, until now...
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Researchers have revealed that Knut, who was raised in an enclosure after being abandoned by his mother at birth, was riddled with medical issues.
The creature suffered a form of autoimmune disease, which caused swelling of his brain.
However, the condition was only discovered in humans eight years ago and has never previously been found in animals.
Scientists at the Leibniz Institute for Zoo and Wildlife Research made the discovery after receiving a tip-off from a neurologist at Berlin's Charite hospital.
They had discovered that Knut's case showed similarities to some of their human patients who suffered from anti-NMDA receptor encephalitis.
Knut is the first non-human subject in which anti-NMDA receptor encephalitis has been demonstrated.
In the journal of Scientific Reports, the researchers say it is very probably far more common than previously assumed, not just in captive or domesticated animals, but also in the wild.
Co-author Prof Alex Greenwood, from the Leibniz Institute for Zoo and Wildlife Research spoke to BBC News and said:
"Pretty much every aspect of Knut's life was played out in the public sphere.
"And reflecting on it now, we're very happy to reach the point where we can end the story by saying why he died.
"There's some closure. Closure for him, but it opens up possibilities for other animals. He will be the trigger for research that may help not just other polar bears but other wild and captured animals as well."
The life expectancy of polar bears in the wild is between fifteen and twenty years however animals in captivity can live even longer because they are not exposed to hunger, thirst or infections.