The royal 'chin rule' you won't be able to unsee.

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If Meghan Markle’s first few months as a Duchess are anything to go by, it’s clear that royal life comes with a lot of rules.

From dress etiquette, to a ban on Monopoly and shellfish, there’s a lot to abide by.

But while the entire British royal family has rules to follow, it turns out the laws of etiquette are even tougher for duchesses Kate Middleton and Meghan Markle.

According to royal etiquette expert Myka Meier, there’s one particular posture rule the two duchesses must always follow.

Speaking to The Sun, Meier explained that Meghan and Kate are expected to always have their chins “parallel to the ground”.

But while the practice sounds a little strange, the reasoning behind it does make sense from an etiquette point of view.

“When your chin points down or up it gives the impression that you’re not paying attention or not interested in what’s happening,” Meier explained.

And as Meier explained, the rule is especially important when walking down the stairs.

"Often walking down a staircase is the grand entrance to a room or event and is the first impression with all eyes and photos on you," she added.

According to Meier, a chin held high may appear arrogant, while holding the chin low could indicate a lack of confidence.

There's even more etiquette rules when it comes to descending stairs.

One particular technique, named the 'Glory Glide', involves keeping the toes pointed slightly towards the bannister (so people at the bottom of the stairs cannot see up your dress) and resting a hand on the bannister rather than grasping it.

Meier also said that in a formal setting, leaning back in the chair or using arm rests is not recommended as both positions can break posture.

"To achieve perfect posture one should keep their back straight, chin parallel to the floor and square the shoulders."

Who knew there was so much to learn?!