The BAFTA outfit was completed with Jimmy Choo heels said to be worth an eye-watering £525 and a beautifully subtle clutch bag.
Kate is patron of 100 Women in Finance's Philanthropic Initiatives and the dinner is in aid of the "Mentally Healthy Schools" project.
But it was the Duchess' glittering shoes we couldn't stop staring at, which appeared to be adorned with hundreds of tiny jewels.
Prince William and Kate got a little bit of adult time, away from the kiddos, last night!
Just look at those shoes.
Kate teamed the jewels with a gorgeous white Alexander McQueen dress with a floral motif.
Earlier in the day, the duchess attended The Royal Foundation's "Mental Health in Education" conference, which brings together delegates from across the mental health and education sectors to work together to tackle mental health issues in schools, per Kensington Palace.
Addressing the crowd she said: 'It's really so exciting to hear everyone here speaking with your wealth of experience about the importance of mental health and particularly the emotional development of our children and teachers.
The event was hosted by BBC presenter Kate Silverton, who welcomed the Duchess: "As you will know [she] has been a great driving force behind the Royal Foundation's work supporting children in their earliest years".