Help! My destination wedding is coming up in October and most of our RSVP's have not come by mail or even email, they have been made in passing through our parents! Just last night my mom informed me that my father's cousin's wife had invited her friend to come along to the wedding. They already invited their adult son and his wife that were not formally invited, but I let that slide, I mean, it's family. But I have no idea who this friend is and have no desire to have un-knowns at my wedding. How would you GRACEFULLY go about explaining that there is no world in which this would be okay and that this person is absolutely not welcome?