Key Takeaways Kate Middleton opted to wear Queen Mary's Lover's Knot Tiara for the state dinner at Windsor Castle on September 17, 2025. The heirloom piece is estimated to be worth $135 million. She accessorized her look with drop earrings that once belonged to Queen Elizabeth and Queen Mary's Lover's Knot Tiara. What Is the Significance of the Lover's Knot Tiara? In 1981, she reportedly gifted the diadem to Princess Diana for her wedding to Prince Charles.