You recently started developing some wrong feelings towards your mother. Seduce her and make sure your father doesn't know about it!
[Disclaimer: this is a work of fiction, all characters are just actors over 18 years old and just playing their roles, all consents have been given, NTR is bad, Loli is bad, yada-yada. Restrain from commenting how degenerate this is. Or you will make me blush.]