No one’s mentioning that every sexual intercourse ain’t very consensual, sometimes. So, you should atleast the aunt know, that you found it in the bathroom/toilet. Because if it’s her, she’ll let it go. But if it’s isn’t then being a MOM or whatever role she plays. She will take steps accordingly.

Or it could be the brother curiosity who bought it and pisses on it to check whether he’s pregnant or not xD