The actor, 51, came face-to-face with Kate Middleton and Prince William at the London premiere of Top Gun: Maverick earlier this month, and revealed on The Tonight Show with Jimmy Fallon that there are "guidelines that are not so much guidelines as hard and fast rules that you are made to follow" when greeting a member of the royal family.
In a separate appearance on Live with Kelly and Ryan, Hamm said, "It's a little anxiety-producing because they give you these rules that you're meant to sort of follow. You're meant to say, 'Your Royal Highness' — if they offer their name, then you can use their name, but you can't do it first. And you can't offer your hand, they have to offer their hand. Then you have to bow, but you can't bow too low."
While Hamm was impressed by Prince William's custom shoes for the premiere, embroidered with F-18 Super Hornets, his costar Miles Teller was more distracted by the Duke of Cambridge's eyes.
"He geeked out a little on Prince William's eyes," Hamm explained to Fallon. "I remember coming back afterwards, he's like, 'They're so blue. I got lost in his eyes.' "
The actor then quipped, "I didn't think we were allowed to look him in the eye."
The monarchy has largely adapted to modern times and many people opt to greet the Queen Elizabeth and other members of the royal family without much pomp — in fact, the British royal family's official website states that "there are no obligatory codes of behaviour when meeting The Queen or a member of the Royal Family." Still, there is a traditional form that many continue to follow to avoid a royal faux pas.
While it's perfectly acceptable to simply shake hands when being introduced to a royal, men may opt to do a slight neck bow (from the head only) while women do a small curtsy.
On presentation to a member of the royal family, the correct formal address is "Your Royal Highness." Then "Sir" or "Ma'am" can be used accordingly.
Prince William, Kate Middleton and Tom Cruise
For the movie premiere, Kate, 40, wore a black floor-length Roland Mouret gown with a white off-the-shoulder neckline shown off by her long hair, which she wore down but tucked behind her ears, which also highlighted her statement earrings.
Prince William, 39, went with a classic black tuxedo and bow tie.
William, who was a Royal Air Force helicopter pilot himself, and Kate were escorted by the film's star Tom Cruise, who offered his hand to the Duchess of Cambridge as she made her way up the stairs.
"We have a lot in common," Cruise said of the prince at the premiere, according to My London. "We both love England and we're both aviators, we both love flying."