The duchess turned up at the event, representing charity Street Child.
Sophie, Countess of Wessex, was also in attendance, representing Brainwave. The royal was photographed making trades in a stylish royal blue dress with high neckline and pearl earrings.
Other celebrities in attendance include Catherine Tyldesley, Nicole Scherzinger and the cast of Modern Family.
Sarah seemed to be in good spirits at the event, with only weeks to go until youngest daughter Eugenie weds partner Jack Brooksbank.
The wedding recently caused a stir in the UK after the huge cost of the event was revealed.
The Mail On Sunday reports Eugenie, who's wedding will occur on Friday, October 12, has invited more than 850 guests.
The Duke and Duchess of Sussex invited just 600 guests to their wedding at the same venue in May.
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