Celebrity Kate Middleton Dazzles in Festive Red Gown and Princess Diana's Tiara at Diplomatic Reception By Kelsey Glein Kelsey Glein Twitter Kelsey Glein is a Seattle-based writer and editor who covers all things fashion, beauty, and pop culture. She was previously the Digital Editor of InStyle and is currently a Social Media Manager at a cosmetics company. InStyle's editorial guidelines Updated on December 8, 2016 @ 05:30PM Pin Share Tweet Email Photo: Dominic Lipinski/PA Wire Kate Middleton makes one stunning lady in red. The Duke and Duchess of Cambridge joined Queen Elizabeth II and other members of the royal family at tonight's annual Diplomatic Reception held in Buckingham Palace, and we couldn't take our eyes off of her festive ensemble. For the prestigious occasion, the Duchess wowed in a sparkling floor-length custom Jenny Packham gown that felt perfectly appropriate for the holiday season. And while the bold color of her dress—which she previously wore for her first state banquet last year—initally grabbed our attention, it was her dazzling crown that had us talking. The headpiece donned by Her Royal Highness was given to Prince William's late mother, Princess Diana, by the Queen on her wedding day to Prince Charles. Called the Cambridge Lovers Knot Tiara, it was worn by the Princess of Wales on a multitude of occasions and is made up of 19 diamond frames with a large pearl drop in each. And in case you're counting, this is only the fifth time that Middleton has been seen in a tiara. She further accessorized her stunning outfit with a pair of statement earrings and a pretty diamond bracelet. VIDEO: Kate Middleton Is Fall Fashion #Goals This Photo of the Royal Family in Ugly Christmas Sweaters Is Everything See more of Kate Middleton's most memorable looks in our gallery.