Endemic to Sri Lanka, it was first discovered in 1937 but had only been seen four time since then.
Scientists last caught a glimpse of the primate in 2002, and believed the elusive animal had since died out.
But field researchers, working with the Zoological Society of London, managed to track down the mysterious creature in the forests of central Sri Lanka.
In a world first, they were able to take pictures of an adult male slender loris sitting on a tree branch.
The field team was able to capture one of the creatures and give it a physical examination, the first time that has ever been done, before releasing it back into the wild.
But experts warned that deforestation in Sri Lanka -- largely blamed on the drive to create tea plantations in the region -- was now the biggest threat to the loris.
Craig Turner, a conservation