One minute you're sweeping through the crowd at your wedding, saying "hello and thank you for coming," to each and every beautiful person you love so much, and the next minute you spot a random, seriously underdressed dude breakdancing on the dance floor with some friend your new hubby went to college with. And that's the moment you realize that, yes in fact, Wedding Crashers are a real thing.
If you're lucky enough to get a head's up pre-wedding that a guest you invited sans plus-one is bringing a random, thank the news deliverer for giving you extra time to deal with the addition. For nearly all other circumstances, put on your game face and hop into gracious hostess mode, because there's nothing that brings a good party vibe down quicker than asking guests to leave.
Step One: Introduce Yourself
If it's a stranger accompanying one of your guests, make it a point to make the uninvited person feel welcome by introducing yourself. Odds are high that this date was a last-minute call-in and they're probably feeling pretty awkward about just showing up at an unknown person's wedding. You're all here to celebrate the same thing, so you might as well nip the awkwardness in the bud from the get-go by extending a warm introduction.
Step Two: Inform the Catering Team
After introducing yourself to the unexpected guest, make a beeline for your catering rep, maître d', or wedding planner. Better yet, have a friend do this task for you. Catering needs to know to set an extra chair and place setting, and they'll want your guidance on where to set them if you have assigned seating in place. There's a good chance this could call for some maneuvering if you have limited chairs per table, but take it in stride and let catering handle the logistics. You might also want to have catering check in with the guest about any dietary restrictions once they're seated.
Step Three: Fahgettaboutit
Relax and enjoy your party! This day is about you and your new partner. It's about the life you're creating together. It's about introducing two families and two sets of friends. It's about the community you're creating together. So, you got a few surprise friends thrown in? At this point, the more the merrier! There's nothing gracious about a "price per plate" attitude, and most likely you've probably already set your final guest count with catering anyway, so the extra plate shouldn't be a problem.