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With St. Patrick’s Day quickly approaching, it’s only right this weekend to turn our attention toward a British royal brooch with a major connection to the holiday: the Irish Guards Brooch.

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Although the brooch appears to be a smooth golden shamrock when viewed from a distance, close-up photography reveals that the brooch’s surface is textured. A single emerald is placed at the center of the shamrock. Various tales have been told about this brooch’s provenance over the years, but we seem to know for sure that it belongs to the Irish Guards and is loaned out to royal ladies who are associated with the regiment.

For example, the Princess Royal wore the brooch on St. Patrick’s Day for several years when she handed out shamrocks to the regiment, as you can see in the image above from 2009.

The brooch itself may date to 2000, when the regiment celebrated its hundredth birthday. That year, the Queen Mother, who presented shamrocks to the regiment on St. Patrick’s Day each year, also celebrated her hundredth birthday. It seems that the brooch may have been created (at least partly) in her honor. The Queen Mother appears to be wearing the brooch in the photograph above, taken in June 2000 at the Irish Guards Centenary service of thanksgiving and commemoration at the Guards Chapel in London.

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Since 2011, the Duchess of Cambridge has been the exclusive royal wearer of the brooch. (The Duke of Cambridge was made Colonel of the Irish Guards shortly before their royal wedding, and he wore the uniform of the regiment on their wedding day.) Her first appearance in the piece came in June 2011, when she attended a medal parade for the regiment at Victoria Barracks in Windsor.

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She also wears the brooch each year to present shamrocks to the regiment, following in the footsteps of Queen Alexandra, Princess Mary, the Queen Mother, and the Princess Royal. Above, you can see the brooch pinned to her lapel on St. Patrick’s Day 2012.

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And here’s how she wore the brooch on St. Patrick’s Day in 2017. That year, she paired the jewel with earrings made of gold and green onyx — a good pairing for the colors of the brooch.

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Kate has also worn the brooch for events related more broadly to Northern Ireland. In June 2016, she wore the shamrock brooch for a garden party at Hillsborough Castle during her visit with the Duke of Cambridge to Northern Ireland.