One of two polar bears kept at the Philadelphia Zoo was euthanized Friday, the zoo announced.

Klondike, a 34-year-old female bear who was the oldest of any bear kept at a zoo in the U.S., was put to sleep after her veterinarians noticed significant mobility issues. Workers at the zoo noticed that she was having trouble walking and standing two weeks ago. She was treated for a urinary tract infection, but her condition did not improve. 

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The zoo said in a statement that Klondike lived much longer than a wild bear would have been expected to survive. 

Her companion at the zoo, Coldilocks, has now become the oldest polar bear in the U.S.