Kate Middleton, Prince William's Polo Kiss Compares to Diana, Charles

Kate Middleton and Prince William’s PDA on the polo field calls back to Princess Diana and King Charles’ kisses on the pitch.

The Prince and Princess of Wales, both 41, shared a rare public kiss at the Royal Charity Polo Day at Guards Polo Club on Thursday, smooching each other on both cheeks before Prince William collected his trophy. The embrace was evocative of the PDA his parents shared on the polo field decades earlier, as Diana would similarly support then-Prince Charles at his polo matches during the years of their marriage. The couple would often kiss at the events — sometimes on the lips!

While Prince William and Princess Kate’s latest public display of affection might be an unusual sight, royal etiquette expert Myka Meier that there are no formal rules on royal couples showing romance in public — it's at their own discretion.

"Senior members of the royal family would likely not be told how to interact or when they can or can not show PDA and would be trusted to use their better judgment as to when it's appropriate," the founder and director of Beaumont Etiquette said. "The royals often adjust PDA to mirror the formality of the event they are attending. At a somber or more formal event, we are less likely to see PDA than at a casual event where it would be deemed more fitting."

While the Royal Charity Polo Day is technically an official event for Prince William and Princess Kate, as the charity match raises millions of dollars for causes close to their hearts, the two seem to be more relaxed with affection in the sporty setting as compared to more formal engagements.

Last year, the couple shared a similar congratulatory kiss at the polo match and walked with their arms linked around each other’s backs.

While the Prince and Princess of Wales (the future king and queen!) typically refrain from PDA, they have had a few sweet moments at events in recent months. During the celebration of King Charles' coronation in Scotland on Wednesday, Kate was spotted with her hand on William's backside as she leaned over to chat with him. The touch was reminiscent of another love tap between the royal couple at the BAFTAs in February — as the royal couple walked the red carpet, cameras caught a blink-and-you'll-miss-it moment where Kate patted William’s butt.

Other couples in the royal family are more casual about public gestures of affection.

Last summer, Meghan Markle and Prince Harry leaned in for a sweet kiss at the Santa Barbara Polo & Racquet Club in California where Harry was playing. The Duchess of Sussex tenderly held her husband’s face during the embrace, and the affectionate gesture called back to the loving kiss they shared after Harry won the Sentebale Polo Cup in 2018.

Likewise, Prince William and Prince Harry’s first cousin Zara Tindall and her husband Mike Tindall don’t shy from showing affection at social sports events. Cameras caught a cute moment between the couple at the Royal Ascot in June, where Mike gently helped his wife remove something from her eye as they rode in a landau carriage in the Royal Procession parade.

On the larger topic of PDA, Meier previously told PEOPLE that regular couples can take some cues from their favorite royals.

"1. PDA such as a hand on the back or hand-holding shows care and comfort and is a safe bet," she explained. "2. When in a professional role, practice professional behavior. 3. If you ever are engaging in PDA that may make someone uncomfortable, it's best to take it to private quarters. An occasional sweet Sussex peck is one thing; a salacious snog is another!"