At first I thought the dress could possibly be Chanel, but it is apparently:
"...Queen Mathilde wore a floral print silk chiffon midi dress by Giambattista Valli...."
https://1.bp.blogspot.com...al-family-f-belgium-7.jpgMathilde wore it on July 21, 2020, the National Day of Belgium. And apparently she had worn it before, on 10 July 2019

Caroline wore it on May 7, 2019 at the 51th Monaco Flower Contest



With thanks to
https://www.newmyroyals.com/