Kate Middleton, Princes William and Harry Cheer at Olympic Torch Rally!

Prince William, Catherine Duchess of Cambridge and Prince Harry as the Olympic Torch Relay passes through Buckingham Palace, London, England on July 26, 2012 Credit: Tim Rooke/Rex/Rex USA

Let the games begin!

Kate Middleton, hubby Prince William and brother-in-law Prince Harry were front and center outside Buckingham Palace on Thursday afternoon among the throngs to greet the Olympic torch.

After a charity sporting event earlier in the day, the Duchess of Cambridge, 30, changed out of a belted Hobbs "Wessex" dress into casual, sporty gear for the momentous occasion -- a fitted white Olympic polo shirt plus skinny, bright-blue denim.

Flanked by William, 30, and Harry, 27, the Duchess grinned and applauded as the final torchbearer lit a cauldron, according to BBC News.

The trio showed off their own athletic skills Thursday morning at the launch of Coach Core (a sports coaching initiative for 16-19-year-olds), where the Duchess (a lacrosse champ at school) played ping pong and later kicked off her Pied-a-Terre wedges to referee a judo match.

Joked William in his remarks at the event: "Watching me on the football [soccer] field is never a pretty sight -- the expression 'giraffe on ice' springs to mind. . . .Catherine, on the other hand, with a tennis racquet or a hockey stick is something to behold and be aware of."