Workers at the North Carolina Zoo in Asheboro have found their polar bear dead in his den.
Zoo officials said 20-year-old Aquila was found around 7 a.m. Tuesday.
Tests indicated the bear's stomach ruptured and his lungs collapsed.
Ken Reininger with the zoo said Aquila had appeared to be in good health Monday night when keepers left.
Aquila had returned earlier this year from a two-year stay at the Detroit Zoo while the North Carolina Zoo's polar bear exhibit was expanded in an $8.5 million project.
The zoo lost its 21-year-old male gorilla Nik last week. Nik was euthanized after suffering an illness that has not been identified yet.
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