Kate Middleton's gold shamrock brooch has a story behind it.

Kate Middleton wore a teal coat instead of traditional green on St. Patrick's Day.

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She wore a gold shamrock brooch pinned to her lapel, a sentimental royal custom.

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The brooch belongs to the Irish Guards and is loaned to royal ladies associated with the regiment.

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When Princess Mary died, the brooch was purchased by the regiment at an auction.

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