Fans of polar bear Knut flocked to lay flowers outside his zoo enclosure, mourning the sudden death of a bear who burst into the limelight as a cuddly, fluffy cub hand-fed by his keeper.

The four-year-old bear died yesterday afternoon in front of hundreds of visitors, taking keepers, animal experts and fans by surprise.

The life expectancy of polar bear in the wild is between 15 and 20 years, but animals in captivity can live even longer because they are not exposed to hunger, thirst or infections.

The bear was rejected by his mother at birth on 5 December, 2006, along with his twin brother, who only survived a couple of days.

He first attracted attention when his main caregiver camped out at the zoo to give the button-eyed cub his bottle every two hours.

Fan clubs soon sprung up across the globe, including in Japan, the United States and Germany. They followed his every move, including his weight battle - he had a weakness for croissants -- or plans to move to a different zoo.

‘Knutmania’ led to a 2007 Vanity Fair cover with actor Leonardo DiCaprio shot by photographer Annie Leibovitz, as well as a film and plush likenesses.

Though the zoo has never released exact numbers, Knut merchandise including postcards, key chains, candy and stuffed Knuts have brought in hundreds of thousands of euros.

Even after packing on hundreds of pounds and trading in his soft fuzz for yellowish fur, many fans remained loyal. News of Knut's death at around 3pm yesterday spread instantly and internationally via Twitter, Facebook and text messaging.

‘We received condolences from all over the world: Australia, New Zealand, Honolulu,’ bear keeper Heiner Kloes told German news agency DAPD.

He said Knut's body was pulled out of the pool in which he died, after it had been emptied of the most of the water. Experts will conduct a post mortem tomorrow to identify the cause of death.
Some fans already had their own theories.

Nadine Hipauf said she worried somebody may have poisoned Knut - whether on purpose or not.

‘My biggest fear is that somebody may have thrown something in for him to eat,’ she said.

Others claimed that Knut had died of stress, saying he was bullied by the three female bears he shared the enclosure with - Tosca, Nancy and Katjuscha.

‘They should have given him a compound of his own,’ Brigit Krause said. 'The ladies were constantly harassing him.'