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Meghan Markle and Kate Middleton may be living royally, but with the Duchess title comes a lot of rules and responsibility. And now, as if the two didn’t already have enough royal protocol guidelines to worry about, an etiquette expert just revealed to News.Com.Au that they also have specific jewellery requirements too.

Etiquette teacher Myka Meier told the outlet that it’s a big no-no for Kate and Meghan to don notable diamonds during the daytime unless it’s for a “special occasion.” The reason? The crown doesn’t want the family to come across as overly “flashy.”

“Other jewels are worn pre-6 p.m.,” Meier explained. “Before 6 p.m., you’ll see metallics, gemstones, pearls, [and] sapphires.”

While it can’t be confirmed that this is always the case with Meghan and Kate, Meier’s rule does seem to align with what the Duchesses have pulled from their jewellery boxes lately — that is, excluding their stunning engagement rings.

For example, Meghan wore a dainty pair of pearl earrings reportedly gifted by the Queen with relatively small diamond studs on them at the WellChild Awards this week.

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But even with the diamonds, they weren’t nearly as bold as her pricey $12,000 Birks earrings that she chose for the 100 Days to Peace gala on Thursday night.

Related article: Meghan Markle Is Launching A Collection Of Workwear For A Good Cause

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Likewise, Kate Middleton also took a more conservative approach to her jewelry choices when she wore silver hoops and pearl drop earrings to Wimbledon this July.

Related article: Meghan Markle Styles A Woman For Her Job Interview DUring First Royal Patron Visit To Smart Works

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The Duchess saved her bling-y diamond and emerald sparklers for the evening British Academy Film Awards (BAFTAs) in February.

Related article: Meghan Markle And Prince Harry Unveil The Name Of Their New Foundation

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Of course, Kate and Meghan are really the only ones who actually know whether this daytime diamond ban is really a big deal to the Queen or not. Regardless of what regal jewels the two Duchesses choose to put on, they always manage to look gorgeous no matter what.

This article originally appeared on Harper’s Bazaar US