Kate Middleton Dazzles in All Blue at the Garter Day Service at Windsor Castle

Kate Middleton's style a decade into her life as a royal by and large falls into four categories: business cas' duchess, summer duchess, sporty duchess, and formal duchess (she's like a one-woman Spice Girls).

The formulas (btw, they work, there's a reason she sticks to them) are as follows: Business casual involves some variation on tailored pants, a blouse, a blazer, and pointy heeled pumps. Summer involves a sundress and wedged sandals or tennis shoes. Sporty involves specific sport-appropriate attire.

As for formal, we usually see the duchess rocking a single-colored uniform (which allows her to stand out in a crowd), involving a coat-dress by one of her go-to designers, sometimes with a fascinator and/or clutch, and with yet another pair of trusty pointy heeled pumps.

For her latest variation on formal, the Duchess of Cambridge attended the Garter Day service at Windsor Castle in what I will call pansy blue. She wore a coat-dress by Alexander McQueen (per the Daily Mail) with a low collar and a belt, paired with a similar-colored fascinator by Juliette Botterill Millinery, a scalloped clutch, and pointy blue slingback pumps by Aquazzura.

The duchess paired the outfit with blue jewelry by G. Collins & Sons to match her iconic engagement ring.

You can shop some of the pieces from her look below.

Garter Day, also known as the Order of the Garter service, recognizes members of said order, the Knights of the Garter—chosen for their commitment to public service. It consists of a grand procession, during which the Queen and several senior royals wear complicated velvet robes. You won't be surprised to hear that this tradition started in 1348.