But who's been taking fashion tips from whom?
Last month Pippa hit the headlines, when she followed in her sister's super-stylish footsteps by wearing a £385 Issa dress to the wedding of a friend in Scotland - the very same style Kate wore to announce her engagement to Prince William in 2010.
And that's not the first time two stepped out in a suspiciously similar get-ups.
From the scene-stealing dress, to the scarlet floor sweeper, the on-trend trouser and faithful tea dress, Kate and Pippa both have very similar ideas when it comes to their style repertoire.
But which sister wears the looks best? You decide!
Who do you think is the most stylish sister? Kate Middleton or Pippa Middleton? Vote now in the comments box below!