Why Kate Middleton and Meghan Markle aren't allowed to wear diamonds during the day.

It’s not surprising that Meghan Markle and Kate Middleton follow a royal dress code – but we only just learned just how strict it truly is.

Not only are the Duchesses banned from showing their toes and cleavage during their daily outings to charity lunches, speaking engagements and other events – but they’re also not allowed to wear diamonds. (Except for their engagement or wedding rings.)

That’s according to royal etiquette expert Myka Meier, who told news.com.au the royals don’t want to appear “flashy”.

“Other jewels are worn pre-6pm,” the Beaumont Etiquette founder said.

“Before 6pm, you’ll see metallics, gemstones, pearls, sapphires. At night, you’ll see the diamonds come out, and that’s in order to not come across as flashy in your appearance.”

Meghan did, of course, wear diamonds on her wedding day – in the form of the diamond-encrusted Queen Mary bandeau tiara atop her head, as well as in her Cartier earrings and bracelet.

The Duchess of Cambridge, who is often photographed during the day wearing pearl drop earrings, is a fan of stepping out in bold jewellery for special occasions.

One memorable look was the emerald and diamond earring and necklace set she wore to the BAFTAS in February. Many commented it looked similar to the Cambridge Emerald Choker Princess Diana used to wear often.

Meier also told news.com.au the reason behind another style rule we've noticed Kate and Meghan following.

The two women appear to never take off their jackets - no matter how sunny it looks out. Meier explained that's because working royals are told "not to disrobe in the public eye".

Yes, well we suppose that's actually a rule us normal folk sometimes follow as well.

What do you think of Meghan and Kate's style?