No physical interactions between royals and nonroyals!
Well, this will may not be a rule late per se by the monarch of the United Kingdom, but it’s more of a tradition that the commoners in the general public choose to follow. When meeting the royal family members the general public greets them by shaking hands or offers them a traditional bow.
Hence, there is no obligatory code of behavior laid down by the members of the royal family or the monarch herself to follow when meeting the Queen or any other member. In December 2014, Prince William and Kate Milton attended a basketball game and had a photoshoot with the athlete LeBron James. After the match in the photo, LeBron had his hand around Kate and the internet busted by calling him out for breaching the royal etiquettes. Well, from the picture it is clear that Kate is not uncomfortable with that physical interaction, so we guess it’s okay here!