The Sunda clouded leopard (Neofelis diardi) was recognized as a distinct species, separate from the mainland Southeast Asian clouded leopard N. nebulosa, in 2008. Both are Vulnerable species, according to the IUCN.
Based on molecular genetic data, researchers suspected that the Sunda clouded leopard might actually represent two different subspecies, and this has been confirmed by a combination of molecular genetics and skull/dental features. There may be additional differences in coat patterning, but the number of specimens available for inspection is not enough to make a definitive statement.
The two subspecies are geographically separated: the Sumatran subspecies (N. diardi diardi) and the Borneo subspecies (N. diardi borneensis). They were probably isolated from each other after Sundaland land bridges were cut off when sea levels rose after the last ice age.
The BBC has a good summary article including a rare video of the animal from Dermakot National Park in Sabah, Borneo.