CINCINNATI (AP) — Officials at the Cincinnati Zoo say a 16-year-old gorilla has died.

The zoo says in a Facebook post that the female silverback, Anju, died from heart failure Wednesday.

Zoo officials say they noticed the gorilla becoming lethargic and gaining weight late November. An ultrasound showed Anju was suffering from a congenital, terminal heart condition.

Primate curator Ron Evans says the gorilla has a 2-year-old daughter, Elle. He says young gorillas typically stay with their mothers until they are 6 years old.

Evans says the zoo is currently working to re-introduce Elle to her gorilla group. He says Elle has an adoptive mother, two age-related siblings and a protective father. He says the re-introduction process must be taken slowly, but the zoo’s outlook is hopeful.