I read a letter in the paper from a boss whose PA had this problem. HR, personnel, could step in on this, but as he didn't have such a dept it was suggested another woman tell her. Can see it might make a difference to get the same sex to have a quiet word but it is a job for someone tactful who can get the message across in a kind and helpful way.
His problem may be caused by lack of hygiene, diet, or he may have a physical problem requiring a chat with his GP. Whatever, he must be told for his benefit and his colleagues. He may well be mortified he has this problem.
Have met a couple of smellies in my time and they dont seem to respond to hints, or in the case of a girl at school, loading her desk with lovely products or, finally, a 'you stink' notice. Kids can be so cruel!