Arriving at the London Palladium theatre, the mother-of-three looked simply stunning in a black lace gown with a low-scooped back by favoured designer Alexander McQueen.
Last year, the Royal Variety Performance was attended by Meghan Markle - who was pregnant with Archie at the time - along with Prince Harry.
Meanwhile Prince William - who was looking handsome in a sleek tuxedo - chatted with the West End cast of Mary Poppins who were opening the show for Variety before their opening weekend at the Prince Edward Theatre in London.
The Duke of Cambridge was even overheard saying: "I love Mary Poppins!"
According to Royal correspondent Rebecca English, when Kate was asked why she didn't bring her three children to the show Kate replied: "They would love it, but not on a school night."
Kate Middleton and Prince William have three children, Prince George, 6, Princess Charlotte, 4 and one-year-old Prince Louis.