Japan's oldest chimpanzee, Johnny, has died at the estimated age of 69, a zoo in western Japan said Tuesday.

The African-born male chimp had seen his appetite diminish since around September, while he had been staying inside his sleeping chamber since 2017 due to age-related health issues, according to Oji Zoo in Kobe.

[Photo courtesy of Oji Zoo]

A zookeeper found him dead on Tuesday morning, and Johnny is believed to have died of natural causes, said the city-run zoo.

Since arriving at the zoo in 1955 at the estimated age of 5, Johnny produced a total of nine offspring with five partners. His first baby, born in 1963, is known as the country's first chimpanzee raised artificially.

"The average lifespan of chimpanzees is believed to be 40 to 50 years" so he had quite a long life, a public relations official of the zoo said.