To be accurate, this is a Golden-bellied Mangabey (Cercocebus chrysogaster) and not an Agile Mangabey (Cercocebus agilis) at all, as the two taxa were split some time ago.
You didn't read the last part of what I said, did you?
The two species have been split, and thus the Golden-bellied Mangabey(Cercocebus chrysogaster) now has full species status and is no longer deemed a subspecies of the Agile Mangabey.