Kate complemented the couture gown with the Cambridge Lover's Knot tiara, which was given to Diana as a wedding present from The Queen in 1981.
She also wore the the King George VI and Queen Elizabeth Bandeau Necklace, a V shaped diamond and ruby collar ending in a diamond drop pendant.
It was Kate's third time wearing the stunning tiara.
Queen Letizia wore a stylish red lace off-the-shoulder gown for the occasion, while Queen Elizabeth wore a white silk gown with pale blue embroidery.
This article originally appeared on InStyle Australia