"Excuse me! In spite of your mother's husband's demise, your father is still fishing off the end of Brighton Pier."

There was a piece in the New Yorker recently about DNA testing and genealogical research, in which the author discussed just such a scenario, absent the fishing reference. Apparently, in the field of such research, the situation described, wherein the biological father and the mother's husband are not the same non-woman, is known as a "non-paternity event."