The navy Dior slip dress that Princess Diana wore to the 1996 Met Gala is widely considered one of the best fashion moments from the annual Costume Institute benefit. But the late royal almost didn’t walk the red carpet in the slinky, silky number—and the reason why shows her dedication to Prince William and Prince Harry . In the Hulu documentary In Vogue: The '90s, former Dior creative director John Galliano reflected on the historic and “real, real fun” process of preparing Diana for her one and only Met Gala. “I remember one day we all jumped into this old van, and we went to London, where we met Princess Diana,” Galliano recalled. “It was like a blessing. I mean, wow.” Her original navy, lace-trimmed slip dress included a corseted detail, and apparently, it was so “ravishing” that the princess feared 14-year-old Prince William would be embarrassed by the outfit, per the Daily Mail .…