Polar bear Knut died of drowning in Berlin Zoo
German polar bear Knut drowned when he fell into a pool of water in his enclosure after collapsing because of a brain swelling, experts have said.
First indications from post-mortem examinations at Berlin Zoo had revealed "significant changes to the brain".
Senior vets now say these changes were probably caused by an infection which caused the bear's brain to swell.
Four-year-old Knut died suddenly at the zoo in front of hundreds. Large amounts of water were found in his lungs.
"We believe that this suspected infection must already have been there for a long time... at least several weeks, possibly months," Achim Gruber, a professor of veterinary medicine at Berlin's Free University, said.
He added that even if Knut had not fallen into the water, it is likely that he would not have survived. A pathology team will continue to search for the exact cause of the illness over the coming weeks.
Knut was hand-reared by zoo keepers after being rejected by his mother, formerly a circus bear in East Germany.
Knut has generated more than 5m euros (£4.4m; $7m) in extra income for Berlin Zoo since his birth, in a craze known as Knutmania.
Reports that he may be stuffed and put on display at Berlin's Museum of Natural History, as part of an exhibition on climate change, have prompted some anger among his fans.
Reuters reports that a "Stop the Stuffing of Knut" demonstration is planned in front of the zoo on Saturday.
Polar bears can live for 15 to 20 years in the wild, and even longer in captivity.