4/10
Kate and Pippa Middleton enjoyed a sisters' night out in London back in 2008. Photo: Mark Milan/FilmMagic
5/10
In 2006, Kate and Pippa did some sister bonding on the sidelines as they watched Prince William compete in a polo match. Since becoming a Duchess, Kate has remained close to her sister and family. They have even continued their trips to Mustique with the Middletons. Photo: Indigo/Getty Images
6/10
Pippa was right there for Kate and Prince William's royal wedding in April 2011 – and when it came time for Pippa to marry James Matthews in May 2017, the Duchess stepped up to do the same. Photo: Pascal Le Segretain/Getty Images
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