Ozzie, the world’s oldest male gorilla, has died at the age of 61, Zoo Atlanta announced on Tuesday. The 350-pound western lowland gorilla was the oldest at Zoo Atlanta and the third oldest in the world.

Ozzie’s cause of death is not yet known. According to a statement from Zoo Atlanta, Ozzie starting exhibiting decreased appetite on Jan. 20. In the day before he died, he was receiving treatment for symptoms including facial swelling, weakness and the inability to eat or drink.

A necropsy, which is the non-human equivalent of an autopsy, will be performed through the Zoo’s partnership with the University of Georgia Zoo and Exotic Animal Pathology Service in the College of Veterinary Medicine and should provide more information on Ozzie’s condition. Zoo Atlanta intends to share these results once they are available.

“This is a devastating loss for Zoo Atlanta,” said Raymond B. King, Zoo Atlanta's president and CEO. “While we knew this time would come someday, that inevitability does nothing to stem the deep sadness we feel at losing a legend. Ozzie’s life’s contributions are indelible, in the generations of individuals he leaves behind in the gorilla population and in the world’s body of knowledge in the care of his species. Our thoughts are with his care team, who have lost a part of their lives and a part of their hearts.”

Ozzie was the only surviving member of the original generation of gorillas who arrived at Zoo Atlanta with the opening of The Ford African Rain Forest in 1988. In 2009, he became the first gorilla in the world ever to participate in a voluntary blood pressure reading.

Ozzie is survived by a daughter named Kuchi, sons Kekla, Stadi and Charlie; granddaughter Lulu; great-granddaughter Andi, and great-grandson Floyd, who all live at Zoo Atlanta.

His legacy also includes children, grandchildren, and great-grandchildren living at other accredited zoos in the U.S. and Canada. Ozzie has more than 20 descendants in total, according to the zoo.

In a statement on Facebook, Zoo Atlanta said Ozzie’s incredible longevity is a testament to the care, expertise, and innovations of their Gorilla Care Team, which has become renowned for the care of geriatric gorillas.

“No matter how many years we get with our animals, it’s never long enough,” said Jodi Carrigan, Associate Curator of Primates. “We made every minute count with Ozzie, and he will always live on in our hearts.”