When encountering a British monarch, a bow or curtsy is okay, a hug generally is not, and “Your Royal Highness,” is much preferred over saying “Chuck” or “Kate.”
Royal Etiquette 101: A primer for President Trump’s visit to Britain

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When encountering a British monarch, a bow or curtsy is okay, a hug generally is not, and “Your Royal Highness,” is much preferred over saying “Chuck” or “Kate.”