1 of 24 Full Screen Full Screen Autoplay Autoplay Close Skip Ad × Caption Buy This Photo Pat Lampi, the current executive director of the Alaska Zoo holds the polar bear cub, Ahpun, on April 23, 1998. (Bob Hallinen / ADN) Wait 1 second to continue.

Ahpun, the beloved female polar bear who lived for two decades at the Alaska Zoo, died unexpectedly on New Year's Eve, zoo officials said Tuesday.

Zoo staff found the bear's body during a routine check Sunday morning, said Patrick Lampi, the executive director. She was about 20 years old.

"She's been a favorite here for generations of people," Lampi said Tuesday. "It's heartbreaking."

A star attraction for the zoo, Ahpun had showed no signs of wavering health, Lampi said. He said it isn't yet known why the bear died. An initial necropsy was inconclusive, and tissue samples have been sent to a lab for further examination. Polar bears can live up to about 40 years in captivity, according to the zoo.

Known as an easygoing, contented animal, Ahpun came to the Alaska Zoo in 1998. She was orphaned when a hunter shot her mother in self-defense near the Northwest Alaska village of Point Lay.

Her name is an unintentional misspelling of "apun," an Inupiaq word for "snow," Lampi said.

For her first few years at the zoo, Ahpun lived with a female brown bear named Oreo. The two arrived at the zoo around the same time. It was unusual for a polar bear and a brown bear to live in the same enclosure. The young bears gained international fans with antics that included wrestling in tubs.

But zoo officials ended the pairing when Oreo became aggressive toward the mellower Ahpun.

In 2007, Ahpun got a new roommate: a younger male named Lyutyik, also known as Louie, who was born in St. Petersburg, Russia, and came to Anchorage from Sea World Australia.

Zoo officials hoped that Ahpun would mate with Louie and give birth to a cub. In recent years, the zoo upgraded its polar bear exhibit to include a maternity den. Despite breeding activity and the exhibit changes, Ahpun never became pregnant.

When she died, Ahpun weighed a little over 700 pounds. Her body parts will be transferred to the U.S. Fish and Wildlife Service and used for research to help captive and wild bears, Lampi said.

"She was a gorgeous bear," Lampi said. "Think of an iconic picture of a polar bear."

The zoo planned to hold a birthday celebration for Ahpun and Lyutyik on Jan. 20. The celebration happens every year, a nod to the timing of polar bear births in the wild, which usually happen in January or February. At one party in 2014, Ahpun stood on her haunches and pawed energetically into a fish-packed, three-layer snow cake.