SEATTLE (KOMO) — The Woodland Park Zoo in Seattle says its only male lion, Xerxes, had to be euthanized because of kidney failure. He was 14-years-old.

According to the zoo, the geriatric lion had been undergoing treatment for possible kidney disease. He was scheduled for an examination next week, however, earlier this week his health quickly began to decline.

“While we were waiting for test results, signs of kidney disease in our geriatric lion were becoming more apparent,” said Dr. Rob Browning, associate veterinarian at Woodland Park Zoo. “His appetite had improved, and he was brighter. However, during another exam yesterday to administer more fluids and medications, his kidney values had worsened suggesting end-stage kidney failure, and we made the humane decision to euthanize him.”

Xerxes was a South African lion subspecies known as the Transvaal lion. He arrived at Woodland Park Zoo eight years ago as part of a breeding program. In 2014, he became a father to three cubs. They were the last cubs to be born at the zoo.

In 2015, two African lion subspecies were listed under the Endangered Species Act. As few as 20,000 to 23,000 African lions are estimated to remain in the wild.