For starters, it doesn't actually belong to the royal family.

By Meghan Overdeep
March 19, 2019
Kate Middleton Shamrock Brooch
Credit: Samir Hussein/Getty Images

On Sunday morning, the Duke and Duchess of Cambridge celebrated Saint Patrick's Day by honoring the decades-old tradition of presenting shamrocks to the Irish Guards.

Dressed in a festive green coat, the gilded shamrock brooch fastened just above the Duchess' heart was unmissable. On anybody other than Kate Middleton, you'd probably assume that a pin of this sort was simply a run-of-the-mill, holiday-appropriate accessory. But this is no ordinary brooch.

True, the Duchess of Cambridge has an extensive collection of priceless jewels, but as Town and Country points out, the shamrock brooch isn't one of them. In fact, it doesn't belong to the royal family at all. The shamrock brooch, which has been worn exclusively by the Duchess since 2011, reportedly belongs to the Irish Guards.

According to jewelry blogger Ella Kay, the brooch, which features a single emerald at the center of the shamrock, "is loaned out to royal ladies who are associated with the regiment."

Princess Anne Shamrock Brooch
Credit: Ferdaus Shamim/Getty Images

Though the details around the prized piece have long been a subject of speculation, we're inclined to believe the account of James Wilson, the author of Up the Micks! An Illustrated History of the Irish Guards, which features a foreword by the Duke of Cambridge. According to Wilson, the brooch was crafted by Cartier and presented to Princess Mary, the Princess Royal, by the regiment in 1961. When Princess Mary died in 1965, the regiment purchased the brooch at an auction of her personal jewelry. It was then worn by the Queen Mother.

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Since then, the piece has graced the ensembles of the Queen Mother in 2000 and Princess Anne in 2005 at events related to the Irish Guard. Kate Middleton is believed to have debuted the shamrock brooch at the Victoria Barracks in June of 2011, during a presentation of service medals, and has been its sole wearer ever since.