The Greater Vancouver Zoo was forced to put down an 18-year-old African lion after an inoperable tumour was found in his chest.

Nagy, who was transferred from the Okanagan Game Farm in 1999, was euthanized at around 2 p.m. Wednesday.

"It's always extremely hard any time we have a death," zoo spokeswoman Jody Henderson said. "We get very attached very quickly to our animals in the zoo, and it makes for a very hard time."

The lion's keepers noticed Nagy had lost his appetite, was lethargic and having difficulty breathing over the weekend.

Henderson said it's too early to tell whether Nagy had cancer, but that it's a possibility. "Animals are no different from humans, lots of cancers around these days," she said.

"As soon as we have the results of the post-mortem, we will release them."

Nagy had two mates during his lifetime, producing three litters with a total of nine offspring. Two of his daughters, Mali and Kali, remain at the zoo.

According to the zoo, wild African lions are hunted for their coats and teeth and are listed as "vulnerable" conservation status by the International Union of Conservation of Nature.