Princess Kate is nothing short of a royal style icon. Since she joined the royal family in 2011, the Princess of Wales, 42, has been the ultimate one to watch when it comes to British royal fashion.
Aside from her plethora of stylish daytime looks ranging from power suits to laid-back trainers worn to community-based public engagements, Prince William's wife possesses an unrivaled ability to rock a royal heirloom tiara at historic and widely-documented occasions.
But there is a secret rule that the future queen must follow when it comes to tiara-wearing and it is an area of protocol that has flown under the radar.
Royal rule
Tiaras are only to be worn in the evening. It goes against royal protocol for Princess Kate or for any permitted royal tiara-wearer to sport the glistening headwear in the daytime. This means that even the most important of events that happen during the day call for other accessories to adorn the royal's pristine updos, whether that be a hat, fascinator, or headband.
Who can wear royal tiaras?
This is not the only rule that the Princess has to follow when it comes to sporting the finest of tiaras, and in fact, the second rule applies not only to Prince William's wife.
Age-old royal protocol dictates that only married royal women can wear tiaras, meaning the likes of Duchess Sophie of Edinburgh and Princess Anne are welcome to join Princess Kate in tiara-sporting, but even 'princesses of the blood' Princesses Beatrice and Eugenie, couldn't wear one until their wedding days.
Rule-breaking brides
The exception to the rule when royal ladies can wear tiaras is on their wedding day. Princess Kate has refrained from wearing a tiara as part of her daytime wedding guest attire but did, of course, wow in an heirloom piece from Queen Elizabeth's collection on her wedding day.
The mother-of-three stunned in the Cartier Halo tiara which is made up of 739 brilliant-cut diamonds and 149 baguette diamonds.
Prince Edward's wife Duchess Sophie wore the breathtaking Anthemion wedding tiara, which was also a gift from the late Queen and was made from Queen Victoria's jewels. She has since re-worn the piece as a wedding guest to the nuptials of Crown Prince Haakon married Crown Princess Mette-Marit in 2001, and again in 2004 when Queen Mary and King Frederik of Denmark tied the knot.
Meanwhile, Princess Anne rocked the dazzling diamond-adorned Queen Mary fringe tiara when she married her first husband Mark Phillips in 1973 - the same wedding tiara worn by her late mother and by Princess Beatrice in 2020. She has since worn beautiful tiaras at state banquets.
Princess Kate's best tiara-wearing moments
Over the years, the Princess of Wales has wowed in several tiaras, including most recently the Strathmore rose tiara to the State Banquet at Buckingham Palace held last November to welcome the Korean President Yoon Suk Yeol and his wife Kim Keon Hee.
DISCOVER: Princess Kate and Queen Mary's twinning tiara moment that went unnoticed
Kate also wore the Lotus Flower tiara in 2022 to the annual Reception for Members of the Diplomatic Corps at Buckingham Palace and the Cambridge Lover's Knot when King Charles welcomed the president of South Africa to Buckingham Palace.