Kate, Pippa Middleton Have Girls' Day Out at Wimbledon

Pippa Middleton and Catherine Duchess of Cambridge at the Wimbledon Tennis Championships Mens Singles Final. Credit: Ray Tang/Rex / Rex USA

The Middletons do Wimbledon!

On Sunday, Duchess Kate went to day 13 of the Wimbledon Lawn Tennis Championship in London -- and this time, her date in the royal box wasn't hubby Prince William, but scene-stealing sister Pippa Middleton!

Clad in a Joseph dress featuring grosgrain trim and ruching at the waist plus a new acorn pendant necklace, Kate, 30, beamed next to her little sister, 27, as they watched the final match between Switzerland's Roger Federer and Brit player Andy Murray. Also on hand at Wimbledon on Sunday? Their parents, Carole and Michael Middleton, David and Victoria Beckham and British Prime Minister David Cameron.

(With a "prior commitment" to attend to, Prince William, 30, stayed back home in Angelsey, Wales.)

Pippa (wearing a light-blue print dress Sunday) has been slowly tip-toeing back into the spotlight since her shocking gun scandal back in April -- when she was photographed with pals, one of whom jokingly waved a gun at photographers.

Although Pippa was eventually let off the hook, she's been "advised by her parents to stay out of the spotlight for a bit," a Middleton family pal tells Us Weekly. "She's being careful, thinking twice before she acts or speaks!"