When you have invited guests and another person arrives uninvited what is the proper protocol?

If an uninvited guest arrives, greet them warmly but discreetly assess the situation. If there’s room and resources to accommodate them, invite them in and include them in the gathering. If not, politely explain that it's a private event and suggest they come back another time. Maintaining a gracious and respectful demeanor is key to handling the situation smoothly.