Whether or not the public is a aware, shouldn't the priest deny communion if he knows a parishoner is in a state of sin?
I hope the man stands firm so he might receive treasure in heaven.
If he knows of the person's sin only through the Confessional, he is absolutely forbidden to act on that knowledge. He can act only if the sin is publicly known. Denying Communion on the basis of private knowledge of the person's sin is tantamount to making that knowledge public.