LOUISVILLE, Ky. — The Louisville Zoo says its oldest polar bear has died.

The Zoo says Arki, a female, was 28 years old and died from unknown causes on Wednesday.

Arki came to Louisville in 2011 from the Brookfield Zoo in Illinois.

A news release from the Louisville Zoo says polar bears usually live into their mid-20s.

Arki was considered one of the most prolific polar bears with five successful litters. One of the two remaining polar bears at the Louisville Zoo, 3-year-old Siku, is Arki's grandson.

The other remaining polar bear at the Louisville Zoo is 2-year-old Qannik, a female.

The Zoo says a necropsy will be performed on Arki to determine the cause of death.