Polar bear Knut, whose dramatic last moments were captured on amateur video last month at a Berlin zoo, died by drowning after falling into a pool in his enclosure, an autopsy has revealed.
However, Knut initially collapsed from brain swelling, and experts say it is unlikely that he would have survived even if he had not fallen into the water.
Knut, 4, died suddenly on March 19 at the zoo in front of 600 onlookers, who watched as the bear suffered from apparent painful cramps, his left leg trailing, before falling into the pool. Large amounts of water were later found in his lungs.
First indications from post-mortem examinations on Knut at Berlin Zoo had revealed "significant changes to the brain," possibly due to an infection, the BBC quoted a senior veterinarian as saying.
"We believe that this suspected infection must already have been there for a long time ... at least several weeks, possibly months," said Achim Gruber, a professor of veterinary medicine at Berlin's Free University.
A pathology team will continue to searching for the exact cause of the illness over the coming weeks.
Knut, hand-raised at the Zoologischer Garten Berlin after being rejected by his mother at birth, became an international media sensation, even appearing on the cover of Vanity Fair along with Leonardo DiCaprio.
Fans of the bear, meanwhile, are reportedly planning a protest on Saturday against plans to put his body on display in a Berlin museum.
An open letter to zoo director Bernhard Blaszkiewitz, reported by the Telegraph, says: "Nobody wants to look at a stiff, dead Knut."
One of many angry entries in an online condolence book provided by the zoo reads: "Knut cannot be stuffed. When are you going to get the message!." The entry, by Michael S. continues: "Leave him alone for once! You cannot be serious. Let Knut rest in peace !!!"
A survey of more than 2,400 people published in the Berlin tabloid BZ revealed that 73 percent of those questioned were opposed to the bear being put on show at the museum.
Campaigners charge that the zoo has already made millions from Knut in merchandising and entrance fees, and accuse them of wanting to milk him for more.