Markus Schreiber / File / AP
The 4-year-old cub reportedly collapsed and died on Saturday at the Berlin Zoo.
The world embraced Knut as our own after his mother rejected him shortly after birth. He beat the odds as the only polar bear ever raised by humans, showing an adorable affection toward his Berlin Zoo trainer – and adoptive father – Thomas Dörflein. But Saturday, Knut passed away of unknown causes while alone in the zoo’s polar bear enclosure.
(More on TIME.com: See pictures of Knut and other celebrity polar bears.)
Heiner Klös, a bear expert at the Berlin Zoo, said Knut was swimming in the water at the time, with more than 600 people looking on. NewsFeed can’t imagine their shock when the celebrity bear collapsed. An autopsy will be performed on Knut to determine the cause of death.
“He had a special place in all of our hearts. He was the star of Berlin Zoo.” Berlin Mayor Klaus Wowereit told the Berlin newspaper BZ. He was the zoo’s most-celebrated resident, but Knut rocketed to fame when he appeared on the cover of Vanity Fair, photographed by Annie Leibovitz and appearing alongside Leonardo DiCaprio.
Unlike most stars, Knut never let the fame go to his head, remaining as innocent and cute as ever. NewsFeed plans to mourn this tragic loss by looking back on all the adorable pictures from Knut’s too-short life.
(More on TIME.com: See Knut’s female drama)