An etiquette expert weighs in.
Kate Middleton Jewelry
Credit: Samir Hussein/Getty Images

Another day, another rule for Kate Middleton and Meghan Markle to follow. In addition to not being able to remove their coats in public or wear any color nail polish except for nude, an etiquette expert recently revealed to that the Duchesses must also follow strict guidelines when it comes to their jewelry.

Myka Meier explained that it's frowned upon for Kate and Meghan to don especially blingy diamonds during the daytime unless it's for a "special occasion." Why? Despite their veritable treasure trove of jewels, the Queen reportedly doesn't want the family to come off as "too flashy."

"Other jewels are worn pre-6pm," Meier told "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."

There are, of course, exceptions. Religious and marital diamonds reportedly get a pass. Small, subtle diamonds are also often given a green light.

WATCH: Pregnant Kate Middleton Borrows the Queen's Pearl Choker Once Also Worn by Princess Diana

Meier added that each woman has a "team of aides" to help them dress and keep track of the etiquette rules.

"They have a team who know what is appropriate for the event they're attending," she explained.

And who wouldn't?