Camilla beamed as she chatted to guests and mingled with the crowd.
This year, Anna Burns won the prize for her "incredibly original" Milkman.
Burns took home the £50,000 award for her novel about a young woman being sexually harassed by a powerful man.
The Duchess presented Burns with her award, and the two smiled as they posed for photographs.
Camilla opted for a black crochet dress and turquoise earrings.
The Duchess of Cornwall's appearance comes just days after she skipped Princess Eugenie's Royal Wedding.