When Kate Middleton married Prince William in 2011, her sister Pippa played the role of the beautiful bridesmaid.
But The Duchess of Cambridge was not a bridesmaid at her sister's wedding to James Matthews.
The reason is that etiquette wise bridesmaids are chosen from unmarried women of marriageable age in the bride's family.
And since Kate Middleton has now been married for 5 years, she was not the bridesmaid at her sister's wedding.
Her children, however, Prince George and Princess Charlotte, were a page boy and flower girl at their aunt's wedding.