Kate Middleton is returning the favor.
The 35-year-old royal was by sister Pippa's side as she married James Matthews at St. Mark's Church in Englefield, England, on Saturday, six years after Kate tied the knot with Prince William.
Pippa became perhaps the most famous bridesmaid in the world at Kate's 2011 wedding at Westminster Abbey in London, where, as maid of honor, she held the train of her older sister's Alexander McQueen gown.
Though not officially a bridesmaid, Kate did the same for Pippa, who walked down the aisle in a stunning lace Giles Deacon gown, featuring delicate cap sleeves, a high neckline and heart-shaped detail on the back.
At Kate's wedding, Pippa graciously corralled the young bridesmaids and page boys outside of Westminster Abbey.
Kate -- whose children, 3-year-old Prince George and 2-year-old Princess Charlotte, were a page boy and bridesmaid at Pippa's wedding -- spent a lot of time organizing the kids on Saturday, and was even photographed adorably shushing them before entering the church.
Kate also stood by her sister's side after she said "I do," just as Pippa did for her.
See the sisters as young bridesmaids in the video below.