This isn’t the first time Kate has worn this gorgeous Preen midi dress, the Duchess wore it in red on her recent trip to Canada.
This time around, Kate kept it classic in black, adding an embellished belt and wearing her hair in one of her favourite half-up styles.
Kate finished off the look with a pair of Prada pumps and dazzling diamond earring, believed to be on loan from the Queen.
The Duchess is a patron for the children’s mental health charity.
Earlier in the day Kate paid a visit to the Natural History Museum in London for a High Tea with twenty child “dino-scientists” to celebrate the museum's Dippy the Diplodocus going on tour.
Kate wore a printed L.K. Bennett dress for the occasion where she helped children decorate “dinosaur eggs” and took part in a mini dig for fossils.