ST. LOUIS (AP) — A popular gorilla who spent his entire life at the St. Louis Zoo has died, and a heart condition is suspected.

The zoo on Tuesday announced the unexpected death of Juma, a 27-year-old western lowland gorilla. The zoo says Juma collapsed suddenly about 1:30 p.m. Monday. A necropsy suggested that a heart condition was the likely reason, but further studies are planned.

Juma was diagnosed in 2011 with irreversible heart problems, but he had responded well to treatment over the past four years.