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Lady Louise Windsor, the daughter of Prince Edward and the Countess of Wessex, had a seat next to Kate at the Velodrome.
The little girl has been a favourite with the Duchess ever since acting as a bridesmaid at last year's royal wedding.
And she spent much of her time leaning over chatting to the eight-year-old, no doubt explaining the finer points of the cycling.
A well-known sports enthusiast, who was captain of her school hockey team, Kate was stalwart in her support of Team GB during the Olympics. It seems she plans to throw her weight behind Paralympics GB as well.
Wearing an official Olympic shirt, the popular royal was pictured laughing and talking with Prince William.
The couple's animated appearance came despite their late night the previous evening.
William and Kate attended the stunning opening ceremony, when the Duchess wore a gold coat dress by Danish label DAY Birger et Mikkelsen, previously seen at the weddings of Zara Phillips and Laura Lopes, the daughter of the Duchess of Cornwall.
In the next few days, Olympic cheerleader is also attending the goalball competition for blind athletes, swimming and athletics.
Watch: Prince William takes George to meet his sister
It's a little princess!