@Lafone The female in with him is his daughter Darci. Casey came to Twycross in 2013 from North America. At the time of his arrival they had 0.3. They are now unfortunately down to the last 2. Hopefully they will bring in a new individual.
Unfortunately, Casey passed away recently and according to one of the keepers, Darci has gone to a European zoo. For the UK, I believe it is now only in Kent - Howletts and Port Lympne - that have these animals. The keeper said that Dusky Langurs do not thrive in captivity, but that their numbers are stable in the wild.
