When Princess Diana arrived at the 1987 Cannes Film Festival in a powder-blue Catherine Walker gown, the world saw glamour. But the soft tulle dress carried a deeper meaning: a subtle tribute to Princess Grace of Monaco.

Known for her pastel wardrobe and approachable style, Diana’s icy blue gown echoed the elegance of Grace Kelly—who had died in a car crash just five years earlier, a fate Diana would tragically share a decade later. The gown’s flowing lines and color were inspired by the Edith Head dress Grace wore in To Catch a Thief, filmed along the same Riviera. Diana and Grace had met in 1981, shortly after Diana’s engagement. Grace comforted the overwhelmed young royal in a private moment that left a lasting impression.