Kate Midleton wore a special golden shamrock brooch on St. Patrick's Day but do you know about its storied past?

The Duchess of Cambridge had the beautiful piece pinned to her forest green Alexander McQueen coat while participating in the century-old custom of presenting shamrocks to the Irish Guards.

Read More: Kate Middleton and Prince William celebrated St Patrick’s Day with a pint of Guinness

While the surface of the elegant pin appears smooth it is textured with a single emerald stone placed at the center of the shamrock.

The Brooch reportedly isn’t owned by the Royal family but instead belongs to the Irish Guards and loaned out to royal ladies who are associated with the regiment.

The Queen Mother was pictured wearing the piece in 2000 and following her death in 2002, Princess Anne was seen wearing the pin annually on St. Patrick's Day when she too handed out shamrocks to the regiment.

The Duchess of Cambridge attends the 1st Battalion Irish Guards St Patrick's Day Parade at Cavalry Barracks on March 17, 2019 in Hounslow, England. Image: Getty

The Duchess of Cambridge attends the 1st Battalion Irish Guards St Patrick's Day Parade at Cavalry Barracks on March 17, 2019 in Hounslow, England. Image: Getty

But since 2011, the Duchess became the exclusive royal wearer of the jewelry after attending a medal parade for the regiment at Victoria Barracks in Windsor.

Despite being a popular piece of jewelry associated with the royal family, its origin is still somewhat unclear.

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Some reports cite Queen Alexandra as the first owner of the brooch, but according to “Up the Micks! An Illustrated History of the Irish Guards,” a book written by James Wilson, which features a foreword by the Duke of Cambridge, the brooch was crafted by Cartier and then presented to Princess Mary by the regiment in 1961.

The surface of the pin appears smooth but is textured with a single emerald stone placed at the center of the shamrock.

The surface of the pin appears smooth but is textured with a single emerald stone placed at the center of the shamrock.

After Mary died in 1965, the brooch was purchased by the regiment at an auction of her personal jewelry and was then worn by the Queen Mother.

How did you spend St Patrick's Day? Let us know in the comments section below. 

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The Duchess of Cambridge meets with Irish Guards after attending the St Patrick's Day parade at Cavalry Barracks on March 17, 2019 in Hounslow, England. (Photo by Gareth Fuller - WPA Pool/Getty Images)Getty Images