Kate Middleton Wore a Rare Casual Outfit in Prince William’s Touching Birthday Tribute

A large component of being a member of the British royal family is dressing the part, and for Kate Middleton, Princess of Wales, that requires a fleet of enviable dresses, glittering tiaras, and impeccably tailored ensembles depending on the event. But sometimes, Middleton gets the chance to dress down—and did exactly that in a photo that Prince William posted of her for her 43rd birthday on January 9.