Sweet footage shows the two sisters in matching pastel pink bridesmaid dresses and floral headdresses as they celebrated the big occasion.
The future Duchess of Cambridge, who is referred to as 'Katie' in the footage, can be seen waving and smiling.
When the adorable three-year-old stepped out to attend her little brother, Prince Louis', royal christening the Internet couldn't get over the young royals resemblance to her famous mum.
Rocking a sweet blue floral dress with matching shoes and headband, Charlotte once again stole the show.
While at the christening, the little royal also debuted a brand new hairstyle!
Normally, the adorable princess parts her hair to the side with a swift comb-over, but for her little brother's big day she opted to part her hair down the middle.