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The Knoxville Zoo shared some sad news on Tuesday.

A zoo favorite, Otis the black bear, became sick and died suddenly last week. Veterinarians believe he died of acute onset pneumonia on Friday.

Otis, 15, came to the Knoxville Zoo in 2001 from the Fort Worth Zoo with Milo. The two young bears were found orphaned in Alaska in 1999, and could not be re-released into the wild.

Milo is still at the zoo, along with a female black bear, Ursula. The zoo says the two seem to be aware of Otis' absence, but "are very well-bonded and are adjusting to the loss," according to Melissa McGee, lead black bear keeper.

"He was a very honest bear," said keeper Susan Petrunio. "What you saw is what you got."