Kate Middleton and Prince William rarely show their affection toward each other in public. But there are times when the couple appears to be loved up.

Earlier this week, the Duke and Duchess of Cambridge attended a royal engagement in London. And in a rare public display of affection, Kate was photographed stroking her husband’s arm.

Prince William is talking to a group of people when Kate stroked his arm, and he barely reacted. And in another photo, Kate is laughing hysterically while looking at her husband. It’s evident that the dad of three still has a way of making his wife laugh.

The gesture was quite surprising for royal fans because Prince William and Kate are not as affectionate as Prince Harry and Meghan Markle are in public. As such, seeing Prince Harry and Meghan hugging and kissing each other is no longer unusual for everyone.

Prince William and Kate, on the other hand, have been together for eight years. But their public displays of affection have been limited. According to body language expert Robin Kermode, the royal couple is simply following in the footsteps of Queen Elizabeth and Prince Philip.

“The Queen rarely holds hands with her husband in public and this seems to have set an unwritten precedent for the other royals,” he said. Since Prince William will become king one day, he and his wife need to be careful with how they act around each other when they’re performing their royal duties.

Despite the unwritten rule when it comes to public displays of affection, Kermode said that it‘s evident that Prince William and Kate are emotionally close. This is because the royal couple has never felt the need to prove their love, especially when they’re attending their royal engagements.

“They come across as a strong, independent couple and while they are always on show, they do not feel the need to ‘show’ their love for each other to the world,” Kermode said. Prince William and Kate tied the knot on April 29, 2011, and they have been blessed with three children together.

Kate Middleton, Prince Louis, Prince George, Prince William and Princess Charlotte Catherine, Duchess of Cambridge, and Prince William, Duke of Cambridge, with their children, Prince George, Princess Charlotte and Prince Louis, after Prince Louis' christening at St James's Palace on July 09, 2018, in London, England. Dominic Lipinski - WPA Pool/Getty Images