Kate Middleton and Prince William
Photo: Getty

The Duke and Duchess of Cambridge have been on countless royal engagements together since getting engaged in 2010, but they’ve shown very little PDA during official events in the public eye. (Meanwhile, Prince Harry and Meghan Markle can’t seem to stop holding hands.) However, that briefly changed this weekend during the official St. Patrick’s Day ceremonies.

While meeting the Irish Guards at the Cavalry Barracks in Hounslow, England, Prince William was spotted putting his hand on Kate Middleton’s back. Though subtle, the gesture was a generally unprecedented move from a couple that rarely touches in public.

Prince William and Kate Middleton
Photo: Getty

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The Duke of Cambridge, dressed in military uniform, laid a white gloved hand on the Duchess’ forest green Catherine Walker coat dress (which she was previously seen wearing on their royal tour of Sweden).

Prince William and Kate Middleton
Photo: Getty

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This actually marked the second time the couple snuck PDA into their public appearances last week. The first occurred on Monday during the formal Commonwealth Day ceremony at Westminster Abbey, where William was also seen putting his hand on Kate’s back.

Prince William and Kate Middleton
Photo: Getty

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Why are the Duke and Duchess so skimpy on hand-holding and hugs anyway? There’s no written, formal ban against royal PDA, but the couple refrains from doing so because they’re technically “working representatives of British Monarchy,” royal etiquette expert Myka Meier told People in 2016.

“The couple are likely to show very little PDA, if any, to remain professional during their designated roles abroad,” she added. That’s why you’ll hardly see William and Kate engage in PDA during their royal tours, as well; they’re still representing the crown during those official visits.

The last time royal fans freaked out over the couple’s rare PDA moments was in December, when Middleton placed her hand on William’s knee when they received gold Blue Peter badges. It was questioned whether the gesture was inspired by Meghan Markle and Prince Harry’s PDA-filled engagement interview two weeks prior.

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This article originally appeared on Harper’s BAZAAR US.