WHEN you're a member of the Royal Family, there are certain protocols you're expected to stick to.
Monopoly is banned, unmarried women can't wear tiaras and PDAs are frowned upon - according to these unwritten rules.
Public displays of affection are considered uncouth, which is why you won't see Duchess Kate Middleton and Prince William holding hands or kissing on a public engagement.
But you may have noticed that Meghan Markle and Prince Harry seemed very cosy at the Invictus Games in Toronto last month, despite also having the eyes of the world on them.
So why do the two brothers play by different rules?
Firstly, Meghan and Harry were free to be intimate at the Games because they weren't officially 'at work'.
Because Meghan isn't a member of the Royal Family, she wasn't attending the Invictus Games for business reasons.
When Harry opened the Games and met with officials, he was there in a business capacity.
But when he later watched the Games with his girlfriend, he was 'off duty' and therefore could act as he pleased.
It was the first time the couple had appeared together in public and Harry marked the occasion by planting a kiss on his girlfriend's face, much to the delight of those watching.
Moreover, there isn't a ban on PDA for Royals.
It's more of a question of following the Queen's example, as she rarely held Prince Philip's hand on public engagements.
And this has become an "unwritten precedent for the other royals", Robin Kermode, body language expert, told Mail Online.
"It is very clear that William and Kate are emotionally close, however, they do not seem to feel the need to prove their love - particularly when on official state business," he added.
"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."
Whereas Harry and Meghan are in a much newer relationship, making it hardly surprising that they seem so loved up.
This article originally appeared on The Sun and has been republished with permission.