The 32-year-old princess wore a green Allie coat and Suzannah tea dress for the opening ceremony, accessorizing with LK Bennett pumps and an Avona clutch.
As for the princes, they looked dapper in matching suit jackets and blue pants.
The royal trio took a few moments to speak to race officials, enjoyed a flyover by the Red Arrows and chatted with the cyclists, including British reigning Tour de France champion Chris Froome. They then stood with the rest of the crowd in front of the 18th century stately home Harewood House to hear the French and British national anthems played.
To finish the ceremony, William, 32, and Harry, 29, flanked Kate as she cut the ceremonial ribbon to begin the month-long cycling race.
Kate and William's son Prince George was not on hand to celebrate the start of the prestigious race, but did receive a gift from organizers. A source told Us Weekly the 11-month-old prince was given a personalized, yellow cycling jersey that signalizes the leader during the Tour de France.
— E! Online UK (@EOnlineUK) July 5, 2014
Following the opening ceremony with the royals, Marcel Kittel went on to win the opening 190.5 km first stage of the race to take the race leader's yellow jersey.
Image via YouTube