With Prince William in the Falklands, Kate wore the traditional Irish colour to attend her first solo military engagement in Aldershot, where she awarded shamrocks to Irish Guards.
Proving her finger is is well and truly on the fashion pulse, the Duchess chose a £1,150 knee-length belted coat dress by designer-of-the-moment Emilia Wickstead for her outing.
Once again, Kate turned to milliners Lock and Co. - whose design she wore on an outing with the Queen earlier this month - for a brown felt hat to finish off her ensemble, adding matching brown suede shoes and Kiki McDonough amethyst earrings.
And to accessorise? Kate topped her green-themed look off with a sprig of shamrock and a golden shamrock brooch.
While we fell head-over-heels for Kate's Emilia Wickstead outfit, it seems we weren't the only ones impressed with her stylish St. Patrick's Day look.
Several soldiers fainted while standing to attention during Kate's visit, during which she also met Prince William's instructor at Sandhurst (he wore the red uniform of the Irish Guards on the Royal Wedding day) presented Shamrock to the Guards' furry mascot Conmael, and even enjoyed a glass of Irish sherry.
Today, the Duchess is expected to make her first ever public speech, during a visit to East Anglia's Children's Hospice.