PIC: Kate and Pippa Middleton Reunite for "Happy" Beach Stroll

You can't keep the Middleton girls apart!

On Sunday, Duchess Kate and her sister Pippa Middleton took a beachside stroll together on scenic Llanddwyn Island in Wales. It's one of the rare times that Kate, 30, and Pippa, 27, have been photographed together since April 29, the date of the older sister's wedding with Prince William. (They were last shot together June 12 at the wedding of mutual pal Sam Waley-Cohen.)

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Naturally, the fashion-icon siblings were a little more casual for this weekend outing: The Duchess wore a pale-pink cowl-neck sweater, jeans and tall green rubber boots. Her little sister wore a blue cardigan, ivory shirt, jeans, and cross trainers.

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"The sisters looked happy and relaxed," an onlooker tells Us Weekly of their mid-morning stroll on the famous Welsh island, known in folklore as the home of St. Dwynen, the patron saint of lovers. After touring the rocky island for half an hour, England's most famous sister walked along the coastline, smiling and chatting, before returning to their car.

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The onlooker adds that Kate and Pippa were joined by Alex Loudon, Pippa's on-again beau, and another female friend.