Meghan's best friend Jessica Mulroney's daughter and twin sons will also be in the wedding party.
And Prince Louis has hand-me-downs from his big sister, too.
The adorable shots were taken by the Duchess of Cambridge at their home in Kensington Palace.
Middle children share their experiences as kids and later as grown-ups. Ring any bells?
The princess delighted onlookers by waving as she visited her new baby brother.