That is an odd-looking De Brazza. I recall quite a sizeable selection of old-world monkeys in these cages until comparatively recently. There were several Macaque, Baboon, guenon and mangabey species. The current Mangabeys were in here until these cages were demolished and their current quarters constructed.
The more I look at it, the more I think Sykes' Monkey is the likely ID. Not sure where I got DeBrazza's from (enclosure mislabelled at the time?). For the moment I'll amend it to just 'guenon', I think.
