Winnie, one of two rare white tigers at Singapore Zoo, has died. The 14-year-old female cat had been terminally ill with a worsening tumour in its jaw bone, and the zoo decided to euthanise it on Aug 12 to prevent further suffering, according to a statement issued by the Wildlife Reserves Singapore on Monday.Its brother, Omar, is the only surviving white tiger at the zoo. Jippie, which was from the same family, was put down in March 2012 as it was terminally ill. The three tigers were born around the same time.Here are five things to know about the trio, and the rare species in general:1. They are extremely rareWhite tigers, a sub-species of the Bengal tiger, are extremely rare. Also known as Panthera tigris tigris, they are born without the pigment that usually makes the fur orange. Only one out of every 10,000 Bengal tigers are born this way. The total global population of Bengal tigers has also dwindled, and there are fewer than 2,500 of them now.Native to the forests and grasslands in South Asia, white tigers are so rare that it has not been seen in the wild for decades. About 300 live in captivity in zoos around the world.2. They are not albinosThey are sometimes mistaken for being albinos, but the unusual white coloration is a result of gene mutation.White tigers also have blue eyes rather than the green or yellow-coloured eyes of normal tigers.3. They can weigh up to 300kgWhite tigers can weigh up to 300kg and reach more than 3m in length. They have 30 teeth, the longest ones at 7.5cm. It can reportedly eat 18kg of meat at one go. In the wild, they can live for about 10 to 15 years while those in the zoos usually survive 16 to 20 years.4. The trio arrived here in the Year of the TigerOmar, Jippie and Winnie were born in Taman Safari, Indonesia. They came to Singapore in 2001 as part of an animal exchange programme and to mark the Year of the Tiger. They soon became a star attraction at the zoo.But they were not the first white tigers here. The rare cats made their debut at the Singapore Zoo in 1988 when two arrived from the Cincinnati Zoo & Botanical Garden in the United States on a four-month loan. 5. The trio made headlines for the wrong reasonThe trio made headlines in 2008 when they attacked zoo cleaner Nordin Montong, 32, who had leapt into the tiger enclosure and waded towards them - in full view of shocked onlookers who initially thought it was a show.The Malaysian worker was mauled to death after he went close to the tigers, puffed up his chest and raised his arms. A pathologist noted that he had 90 external injuries, in addition to fractures of the skull, neck and ribs.The incident was ruled a suicide by the state coroner in 2009. Evidence showed that the cleaner had not accidentally fallen into the tiger enclosure, "but had deliberately jumped into the moat, waded through the water...before thrusting his chest towards the advancing tiger with both arms outstretched”, said the coroner. Witnesses who watched the grisly attack also testified that they were certain he had not tried to defend or save himself when the tigers attacked him.A zookeeper who testified in court was of the opinion that the tigers thought Mr Nordin was some sort of toy, as keepers often let the animals play with brightly coloured toys and objects.Following the tragedy, the zoo introduced more safety measures, such as installing emergency alarms and stepping up patrols by zoo keepers and staff members.