The 34-year-old slipped into a delicate grey dress and her favourite nude heels for the lunch reception on Wednesday afternoon (4 May), shortly after visiting Hampton Court Palace to open a new children's playground.
It was her first engagement as a Patron of the Anna Freud Centre, a role she took up in February following her keen interest in children's mental health issues and emotional wellbeing in the UK. She met with families who have benefited from the support on offer, and watched a film about the ambitions of the centre.
Peter Fonagy, Chief Executive of the Anna Freud Centre, said: "I am honoured that the Duchess of Cambridge has chosen to become a patron of the Anna Freud Centre. I'm particularly proud because I have come to recognise just how knowledgeable she is in relation to what is a complex and difficult issue that so few people genuinely understand.
"It is my hope that her future work in this field will serve as a catalyst for all and that we are able to achieve the quality of care that children and their families so richly deserve."
Earlier today, the duchess was at historic royal residence Hampton Court Palace to officially launch the Magic Garden, a new interactive children's playground inspired by the myths and legends of the Tudor period.
Tonight, she'll be at the National Portrait Gallery in London to view the Vogue 100: A Century of Style exhibition. She appears on the cover of Vogue magazine's 100th edition, in a series of photos shot near her Norfolk home by photographer Josh Olins, in collaboration with the gallery.
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