Pretty much every single major celebrity has attended the Met Gala at one point or another, but one person who hasn’t RSVP’d yes? Kate Middleton. The Princess of Wales has never attended the annual gala, despite—allegedly!—being at the very top of Anna Wintour’s invite list, and being no stranger to red carpets: Dave J Hogan // Getty Images It’s not unheard of for royals to attend the Met—specifically Princess Diana, who showed up in 1996 wearing Dior and some seriously major sapphire and pearl jewelry, which Kate owns nowadays! New York Daily News // Getty Images A source tells Rob Shutter that Anna personally asked the Princess of Wales to attend, saying “Kate is the one celebrity Anna wants and cannot get. That is the obsession.” “This was never only about Diana,” the source adds. “Anna wanted Kate because Kate is the ultimate prize.” Another insider alleges that Anna tried to get King Charles and Queen Camilla to convince Kate to attend, and that “Kate understood exactly what was being asked.…