Zookeepers at the Oakland Zoo and fans among zoo-goers are mourning the loss of the zoo's senior lion, Leonard, who had to be euthanized on Sunday. He was 19, and had been suffering from kidney trouble and arthritis.

Raised entirely in captivity, Leonard came to the zoo along with his his sister Sandy in 2000 as six-month-old cubs. The pair had been rescued by the Houston SPCA from a private home, and zookeeper Erica, who raised him from a cub, writes on Facebook, "we were happy to give them a 'forever home' here at Oakland Zoo."

Sandy passed away in 2016 after a bout with cancer, as Erica explains, after which the zoo added three male cubs to its African lion habitat. The trio had to be separated from Leonard by a fence for safety reasons, but he often "socialized" with them through the fence, she says, "either rubbing heads or vocally scolding misbehaving youngsters when needed. He never lost his dominating presence."

Leonard had turned lethargic in recent weeks, and showed little movement, which led the zoo to transport him to an animal hospital late Sunday.

"It’s a big loss for us," says zoo spokesperson Isabella Linares to the East Bay Times. "We hope people can honor his life by supporting lion-conservation efforts to keep those animals in the wild, rather than trying to make them pets."

The zoo says that the wild African lion population has declined 43 percent in the last 20 years, since Leonard was born. That means the species has been listed as "vulnerable" by the International Union for Conservation of Nature.

"Our hearts go out to our Animal Care staff who took tremendous care of this magnificent being, and to Leonard himself," the zoo adds on Facebook. "Rest in peace, beautiful lion."

Photo: Colleen Renshaw