The zookeeper who was a 'surrogate father' to the polar bear Knut has been found dead amid fears that he became depressed after they were separated.
Thomas Doerflein, 44, had been told to stay away from Knut because they were too close.
There were also concerns that Mr Doerflein could be injured during one of their regular wrestling bouts as Knut grew.
Zookeeper death: Thomas Doerflein, who hand-reared Knut the polar bear, has been found dead
Police said the keeper - who was known as Knut's 'stepfather' - had been seriously ill.
They hope a post mortem examination will show how he died at his flat in Germany.
Mr Doerflein raised Knut by hand at Berlin Zoo after the bear's mother rejected him at birth in December 2006.
When animal groups called for Knut to be destroyed rather than hand-reared, Knut became a worldwide sensation and the subject of a film.
Close bond: Doerflein became a father to Knut after the cute cub was rejected by his mother
World famous: Knut hit the headlines when it was said he should have been put down rather than raised by humans
Mr Doerflein, a father of three, lived, ate and slept with him - cleaning him in the morning and cuddling him to sleep.
He nursed Knut in his arms behind closed doors and wrestled with him when he was old enough to play.
When Knut made his public debut in March last year, he and Mr Doerflein started a daily performance for thousands of visitors to the bear's enclosure.
Star attraction: People flocked to Berlin Zoo to see Knut frolick in his enclosure with Doerflein
But the spectacle ended in July when the zoo's director ruled that Knut was too big for Mr Doerflein to play with safely.
Months later he was barred from contact with Knut amid claims he had rowed with bosses over their closeness. Friends said he became depressed.
Knut has since been diagnosed as a 'psycho bear', missing his keeper and addicted to attention.
Zoo biologist Heiner Kloes said Mr Doerflein was one of his best keepers, adding: 'He contributed crucially to the development of Knut. He had passion for him.'
Growing: Doerflein was banned from playing with Knut after he grew in size
Grown: Knut how he looks today
Zookeeper who hand-reared Knut the polar bear found dead | Mail Online