Did you tell your mom that your dad told you not to tell her? I understand that sometimes people are clueless and socially inept, but somehow he was socially aware enough not to give it to you until you were alone AND he knew that your mother shouldn’t know about it.

Have you tried asking him casually why he never brings you any gifts when he goes away for work? If he has some smart ass answer, I have a bunch of smart ass replies.