Knut is no longer cuddly and has become an unpredictable, surly adolescent. Berlin’s celebrity polar bear is now deemed too dangerous to perform in public with the keeper who has brought him up since the cub was rejected by his mother.

Crowds gathered anyway yesterday at the bearpit for the usual 11am performance; in warm weather the keeper and the bear would swim together and later wrestle on the rocks. But when visitors shouted “Knut, Knut!” the polar bear, out of sight and now in a separate compound, started to howl miserably.

“This will be a period of cold turkey for him,” a member of the zoo staff said. “He has become addicted to human laughter and applause.”

Weighing in at 42kg (6st 9lb), Knut has lost his fluffiness and what used to be a playful nibble is now liable to remove a chunk of human bone. “Knut has hurt me a lot,” said Thomas Dörflein, his keeper, whose arms are a mass of bruises and flesh wounds. “You can’t meddle with him when he is having one of his rages or tantrums.”

The decision to stop the daily show, which has drawn more than a million visitors since Knut was born seven months ago, is regarded as the essential first step towards separating him emotionally from humans. “It is time for him to learn to live independently,” Reimon Opitz, a senior keeper, said.

Knut became famous because of his photogenic cuddliness and because his plight seemed to symbolise the need to slow down climate change and the melting of the polar ice-caps. The little bear appeared on the front cover of Vanity Fair, snapped by Annie Leibovitz, and became the subject of pop songs and children’s books. The bear was left to die on a rock in the polar bear compound by his mother, Tosca, a veteran East German circus animal. Keepers scooped him to safety with an extended fishing net and placed him in an incubator. Since then, bottle-fed by Mr Dörflein, he has gone from strength to strength.

Human intervention in his fate prompted debate about whether rejected animals should be saved. German laws state that animals should be brought up by their own species, a measure intended to crack down on abuse in circuses. Several young zoo animals are put down every year because they have been rejected by their mothers.

An animal rights activist, seeking a change in the law, said that, logically, Knut should have been killed too.

That caused outrage across the world. Knut had to be saved, not only because he was fluffy but also because polar bears were under threat as a result of human actions, his champions said. Saving the hapless cub became a way of making amends for warming up the climate. Sigmar Gabriel, the German Environment Minister, declared himself to be Knut’s personal sponsor and is paying for his fish.

Now, after a painful teething period in which he gnawed Mr Dörflein’s gumboots, Knut has sharp teeth. He can jump a metre in the air and propel himself at his keeper with the force of an adult rugby player. He is currently in a pit with other young bears.

First contacts with his father, Lars, were not encouraging: the adult bear threw himself at an acrylic shield, apparently wanting to attack his son. This and other problems await Knut as he approaches adulthood.

Mr Dörflein is taking a long holiday to wean the bear away from his human dependency. The keeper has also become a celebrity and has received several offers of marriage. The final break will come only when Knut is moved to another zoo to mate. “I wouldn’t visit him then,” he said. “If he smelt my scent it would cause him suffering. I wouldn’t do that to him, or to myself.”

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