The pregnant royal, who is expecting her second baby with Prince William next April and has been suffering heavily from morning sickness, looked gorgeous in a Temperley London black knee-length dress.
The dress had on-trend white crocheting throughout, and the Duchess accessorised with black heels and a matching clutch.
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The charity is one of Kate's selected patronages, and the 32-year-old royal looked pleased to be attending the annual event which was held at L'Anima.
The swanky Italian restaurant isn't far from the couple's home in Kensington Palace, making it especially manageable.
Earlier this week, Kate admitted that she was happy to be out of the house, and is clearly enjoying getting back to work.
Looking radiant, healthy and typically chic, Kate didn't put a designer-shoe clad foot wrong at Tuesday's evening do at the Natural History Museum. She wore a new pale blue Jenny Packham creation and Prada heels for the occasion.
Earlier in the day, she was also seen chatting easily with Singapore's President Tony Tan and his wife at the start of their state visit to Britain.
Since announcing the pregnancy in September, the Duchess has been completely out of the limelight. She was forced to pull out of her trip representing the Queen at the anniversary celebrations for Malta's independence and several other causes close to her heart.
Her debilitating morning sickness now appears to be under control but aides are considering each appointment on a case by case basis.