Ever wonder why you never catch a glimpse of Duchess Kate's bra straps? An etiquette expert spills the fashion secret. Royal etiquette plays a big role in Duchess Kate's life, even when it comes to style. For instance, she's not allowed to wear dark nail polish, reveal bare legs or shoulders, and must ensure her neckline is never too low. So, it's no surprise that there are strict rules when it comes to underwear. "Underwear is considered private intimate clothing, which is why Royals should never display it," explains etiquette expert Myka Meier to "The Sun."

But how does Duchess Kate manage to keep her bra straps hidden under thin fabrics and airy lace dresses? Meier reveals the secret on her Instagram account, stating, "There are two ways to conceal bra straps: one is to wear clothing with built-in bras and molded cups. The second option is strapless shapewear, available in nearly every skin tone."