And this is because tiaras should only be worn by married woman and royal brides.
Royal tradition explains why Princess Eugenie and Beatrice are not allowed to wear a tiara like Kate, Duchess of Cambridge, and Meghan Markle.
Both Meghan Markle and Kate were spotted in stunning tiaras on their Royal Wedding days.
And it won’t be long before Eugenie gets her time to shine, when she is expected to wear a fancy headpiece when she ties the knot with Jack Brooksbank in October.
Jewellery expert Geoffrey Munn told how married royals are only allowed to wear the fancy headwear.
He told Cosmopolitan: “Any woman may wear one, but ancient tradition has it that they must be a bride or already married.
“The tiara has its roots in classical antiquity and was seen as an emblem of the loss of innocence to the crowning of love.
“One of the mainstays of European royalty and aristocracy is to do what you have always done and formal dress, jewellery, and tiaras are just a part of this.”
Princess Eugenie has never worn a tiara in public before, although it is expect that she will on her big day – as most royal brides tend to do.
It is expected she will wear her mother Sarah Ferguson’s tiara.
The Duchess of York’s tiara was a gift from the Queen for her wedding day to Prince Andrew.
The headpiece, from Garrad, the same designer who created Sarah engagement ring, was part of a demi-parure, a set of jewellery with typically three pieces – and this one had a necklace, earrings, and a bracelet.
The Duchess of Sussex wore the Queen Mary’s Lozenge Bandeau tiara during her wedding to Prince Harry in May.
The Queen Mary’s Lozenge Bandeau is an art deco style tiara. It belonged to Princess Mary, and has been worn by Princess Margaret.
The diamond tiara hadn’t been seen since it was last worn by Princess Margaret in 1965 until Meghan’s wedding day in May.
Kate Middleton’s wedding tiara was the Cartier Halo Tiara, beforehand referred to as the Scroll Tiara.