The Woodland Park Zoo's beloved silverback gorilla, Leo, died of heart disease, the zoo's director of animal health announced after a necropsy to determine what caused Leo's death last week.

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The 40-year-old silverback gorilla who died last week had heart disease, according to Woodland Park Zoo.

The zoo said a necropsy, which is an autopsy performed on an animal, revealed that Leo the gorilla died from an aortic aneurysm involving a rupture to the main artery leaving the heart.

“The aortic dissection was extensive, extending into the descending aorta, down as far as the lower back region of Leo,” Dr. Darin Collins, Woodland Park Zoo’s director of animal health, said in a Thursday statement.

According to the zoo, heart disease became known as a major cause of death in the early 1990s among all four great apes: gorillas, orangutans, chimpanzees and bonobos.

Because of that, the Great Ape Heart Project was established among the zoo communities, the zoo said.  A more detailed examination of his heart will be conducted, Collins said.

Leo, whose full name was Leonel, was an integral part of one of the zoo’s great ape families that included three female gorillas: 22-year-old Nadiri, her 2-year-old daughter, Yola, and 16-year-old Akenji.

Leo became an adoptive father to Yola after her birth. His body was kept at the gorilla building after his death so his animal and human family members could say goodbye, zoo officials said last week.