Omar the white tiger, one of the iconic animals at the Singapore Zoo, was euthanised on Wednesday due to ill health.

"We are deeply saddened by the passing of our senior white tiger Omar," Wildlife Reserves Singapore (WRS) said yesterday.

"An icon of Singapore Zoo in his own right, he enthralled guests with his majestic presence."

The tiger, which was nearly 18 years old, was closely monitored for the last three years. It developed melanoma, a type of skin cancer, and its joints degenerated, said WRS. A team of keepers and veterinarians provided supportive care to Omar for the past few months to ensure its quality of life was maintained. But due to its worsening health, the "difficult decision" was made to euthanise it, said WRS.

Omar was born in Indonesia's Taman Safari and arrived in Singapore Zoo with two female siblings, Winnie and Jippie, on April 6, 2001, when they were all 19 months old.

In 2008, the three tigers mauled Malaysian contract worker Nordin Montong after he deliberately climbed into the tiger exhibit.

Omar would have turned 18 years old in September. Jippie died in 2012 while Winnie died in 2014.

In the wild, tigers have an average lifespan of between 10 and 15 years, while those under human care live for 16 to 20 years on average.

"We will miss Omar, and our thoughts and appreciation go especially to his caregivers, who for so many years took such great care of him," said WRS.

Singapore Zoo is now home to two white tigers, Pasha and Keysa. The four-year-old siblings arrived from Batu Secret Zoo in Indonesia on Jan 15, 2015.