The stunning former 90210 star attended the star-studded bash with new beau, former Scottish rugby player (and Kelly Brook's ex), Thom Evans.
Jessica wore a glamorous embellished crop top with a high-waisted skirt, adding a dash of colour with a chic red shoulder bag and matching red lippie.
And Jessica added inches to her height with a pair of sky-high platform peep-toes - although 6ft Thom still towered over her!
Jessica and Thom spent the day catching the tennis at Wimbledon and then, after a quick wardrobe change, turned up at the exhibition launch party at Kensington Palace.
Gorgeous Jessica, 24, also showed off her impossibly shiny mane of hair. Out-glossing Kate Middleton at the royal couple's official home? The cheek!
Not that we think Kate would mind. Prince William and Kate Middleton - who are hoping to move into the newly refurbished apartment within Kensington Palace with their new baby this summer - are busy preparing for the imminent arrival of their first child.
The new exhibition, featuring outfits worn by Princess Diana, Princess Margaret and the Queen, is a must-see for fashion fans.
As well as 90210 star Jessica Lowndes, other attendees included Minnie Driver, Henry Holland and Pixie Geldof.
By Amy Cavill