The 'no touching' royals rule looks very uncomfortable for Serena Williams and Kate Middleton
One is the greatest athletes of all the time, the other - a princess and the most photographed woman in the world.
So when Serena Williams met Kate Middleton at Wimbledon, it was a memorable day for both of them.
The Duchess of Cambridge took prime spot during Williams' Wimbledon campaign, enjoying a bird's eye view in the royal box. But after taking home the championship - her 22nd - Serena shared a picture of her meeting Middleton and the Countess of Wessex taken after the semi-final.
And that's when you're reminded of a rule often forgotten when it comes to the British royal family, especially Kate as part of the new wave of relatable royals - there's no touching allowed.
Rules of conduct expected of civilians around the royal family were made public when Kate and Prince William travelled to the US in 2014 - not only were journalists covering their trip required to adhere to a dress code, but celebrities were reportedly told before not to touch either of them.
Remember when NBA LeBron James hit headlines around the world for "breaking protocol" and putting his arm around the Duchess? At the time, etiquette experts declared their collective outrage as royal codes of conduct state there is no touching shoulders, hugs or kisses on the cheek.
So, while Serena and Kate look genuinely happy to be meeting and posing together for a photo, they stand side by side without so much as their elbows touching.