Kate Middleton and Prince William's Low-Key PDA Moment at Boston Celtics Game

It was date night for Kate Middleton and Prince William at the Boston Celtics game!

The Prince and Princess of Wales, who are in the U.S. for a three-day visit leading up to William's Earthshot Prize Awards ceremony on Friday night, shared a rare moment of PDA as they watched the basketball game while sitting courtside on Wednesday.

The couple, who celebrated their 11th anniversary last April, discreetly held hands during the game. Kate was also seen putting a hand on William's knee. They leaned in close and were seen laughing throughout the event.

Although the parents of three usually keep their affectionate gestures out of the public eye, they do occasionally engage in some hand-holding or cheek kisses.

Paul Edwards - Pool/Getty Prince William and Kate Middleton

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Royal etiquette expert Myka Meier, founder and director of Beaumont Etiquette, previously told PEOPLE that there are no formal rules on royal couples being lovey-dovey in public — it's at their own discretion.

Samir Hussein - Pool/WireImage Prince William and Kate Middleton

"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," Meier 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."

Paul Edwards - Pool/Getty Prince William and Kate Middleton

The sports-loving stayed for the entire game, excitedly cheering on the Celtics as they beat the Miami Heat. The next day, William chatted with a group of well-wishers about the experience.

"We had a good night at the basketball last night," he said. "If the Celtics hadn't won last night, we'd never be able to show our faces in Boston again! Quite relieved they won."

Paul Edwards - Pool/Getty Prince William and Kate Middleton

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Ahead of the Earthshot Prize Awards ceremony on Friday night, Kate and William both stepped out on solo outings earlier in the day. Kate visited Harvard University, where she learned about scientific advances to improve the lives of children, while William visited the John F. Kennedy Presidential Library and Museum.