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SAN DIEGO (AP) — A 45-year-old male river hippopotamus named Otis and nicknamed the “smiling hippo” has died at the San Diego Zoo.

Otis had been under care for degenerative joint and spinal disease and a decision to euthanize him was made last weekend when his condition declined dramatically, the San Diego Zoo Wildlife Alliance said intweet Monday.

Otis got his nickname in 2010 because of viral photo taken by a zoo visitor that captured him with his teeth displayed in what looked like a giant grin, The San Diego Union-Tribune reported.

The 4,500-pound (2,041-kilogram) hippo was born in the wild in East Africa and went to the Los Angeles Zoo before being transferred to San Diego in 2009 to mate with a female named Funani, the newspaper said.

“Otis will be greatly missed by wildlife care staff, veterinarians, volunteers, and guests,” the San Diego Zoo Wildlife Alliance said.