The Oregon Zoo in Portland was closed Friday following the unexpected death Thursday night of Lily, a 6-year-old Asian elephant who was considered "the darling of the zoo," according to the park's director.

Lily, the youngest member of the zoo's elephant family, had been diagnosed Wednesday with an active strain of endotheliotropic herpesvirus, but didn't immediately show any symptoms, the zoo said in a statement, the Oregonian reported.

When she was lethargic and uninterested in food on Thursday morning, vets treated her with fluids, medication and a transfusion, but to no avail. Lily succumbed to the viral infection late Thursday night -- one day before her sixth birthday, the paper reported.

"I can't imagine a more devastating loss for this zoo family and our community," zoo director Don Moore said in a statement obtained by the Oregonian. "Lily was the darling of the zoo. She was loved by everyone from her elephant family to the people who cared for her every day to her thousands of fans.”

"I can't imagine a more devastating loss for this zoo family and our community. Lily was the darling of the zoo. She was loved by everyone from her elephant family to the people who cared for her every day to her thousands of fans.”

— Don Moore, director, Oregon Zoo

Her mother Rose-Tu and people who cared for her since birth surrounded Lily when she passed, a statement on the zoo's Facebook said.

"Veterinary and care staff did all they could to save her, and Lily fought hard to the end," the statement said. "Lily brought joy to everyone she encountered. This is a heartbreaking loss for the herd and our entire community.

The Oregon Zoo was closed all of Friday, including for the scheduled evening ZooLights. It was to reopen Saturday, Fox 12 Oregon reported.