But, royal fans also noticed that Prince William had seemingly taken notes from little brother Prince Harry and new wife Meghan Markle.
While walking into the Summit, the 36-year-old royal placed a loving hand on Kate's back - a move the Duke and Duchess of Sussex have become known for.
While there is no official "protocol" barring royal couples from showing affection in public, etiquette expert Myka Meier told PEOPLE, "it’s all simply a matter of preference for each couple and is also likely dependent on the nature of the event they are attending."
“They are not afraid to hold hands. They don’t mind showing their emotions,” veteran royal photographer, Mark Stewart, also told PEOPLE.
“Meghan is used to being touchy-feely, and Harry is the same,” former palace spokesman, Dickie Arbiter, also told PEOPLE. “Harry has always been tactile.”
“While Prince Harry and Meghan holding hands is atypical for royal engagements, it is a seemingly welcomed gesture to show unity and celebration of their engagement period,” royal etiquette expert Myka Meier, founder and director of Beaumont Etiquette, said. “There is no protocol that says they can not show affection on official engagements, and this gesture makes them relatable and loveable to the public.
“Meghan and Prince Harry holding hands at a royal engagement is a refreshingly modern approach to their new role both as a couple and as representatives of the royal family.”