Koko was reunited with his keeper, Dragan Trajkovski, on Thursday, who said he was overjoyed to see the chimp again.
"It was a joy I cannot describe," the 49-year-old told The Associated Press. "After 10 years, Koko recognized me. We touched each other, he turned his back for a little scratching and pursed his mouth in a chimp kiss."
Koko was born in the zoo of North Macedonia's capital Skopje in 1995. His mother died of tuberculosis two years later, and the young chimp began suffering from depression and loneliness. Trajkovski tried parenting him but for years his condition did not improve.
Eventually a Netherlands-based animal rescue group, Animal Advocacy and Protection, was contacted and Koko was transferred to their facilities in the Netherlands in 2009 to recover.
After 10 years at the AAP facility, Koko returned to Skopje along with three other chimpanzees who will be keeping him company: 57-year-old Mimmi, and Hiasl and Rosi, both 38. All three were treated by AAP after suffering years of mistreatment. Mimmi was once in a circus before ending up living in a drab enclosure in a garden center in Germany, AAP said.
"I feel like my kid is back," Trajkovski said.
Hiasl and Rosi were two of 12, 6-month-old chimps sent as cargo from Africa to Vienna in 1982. Austrian authorities confiscated them at the airport due to a lack of correct documents, and only three of the 12 survived. Hiasl and Rosi were transferred to AAP and the third, a chimp named Henry, was sent to a German zoo in 1985, where he lived until his death in 2015.
A special enclosure has been created for the four chimps in Skopje zoo, including a special two-story house and an outdoor area, AAP said, and a team of Skopje zookeepers along with AAP professionals will monitor them.
The four chimpanzees have been put in a 20-day quarantine and will be available for the public to see at the zoo from the beginning of August.
"We are happy to have Koko back from a period of re-socialization," Skopje's mayor Petre Shilegov told reporters on Thursday.
Skopje's zoo spokeswoman, Tina Mickovska, noted chimpanzees are an endangered species. From one million, their population has dropped to an estimated 170,000 to 300,000 individuals, according to the International Union for Conservation of Nature, or IUCN.
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