And it appears the Duchess may have been inspired to wear the £320 dress by Paris Hilton, who stepped out in the same design at the amfAR gala in Los Angeles one week earlier.
The Duchess of Cambridge looked gorgeous in this Self-Portrait dress
Both Kate and Paris looked gorgeous in the long-sleeved gown, and showed off their individual senses of style by accessorising it in completely different ways.
While Kate, 34, paired hers with suede Gianvito Rossi heels, a Mulberry clutch and delicate pearl earrings, Paris opted for white heels, a crystal headband and statement drop earrings.
We can see why Kate and Paris chose to wear the dress; with pretty crochet detailing and floral neckline, and a daring split in the pleated full-length skirt, it is a failsafe choice for easy glamour.
Paris Hilton wore the same dress last week
The Duchess wore the dress to attend the premiere of A Street Cat Named Bob in her capacity as patron of Action on Addiction, the charity that helps those suffering from problems of addiction.
Kate had the opportunity to meet the stars, cast and crew of the film, including Luke Treadaway and of course, Bob the cat!
Earlier in the evening Kate watched highlights of the Recovery Street Film Festival, which features inspiring films made by former addicts and their loved ones about life in recovery from addiction.
Kate learned about the creation of the festival, before watching the three prize-winning films and later meeting both the prize-winners and representatives from some of the charities involved in the festival.