For the outing mum-to-be Kate wore a brown silk animal print dress by high street brand Hobbs, which she teamed with black tights and heels.
Prince William's wife previously wore the chic dress under a pink coat during a visit to Wales last year and then again on Christmas Day 2014.
Youngsters and royal fans who had gathered outside cheered as the expectant Duchess arrived at the London charity to learn more about fostering and the need for more carers.
"Today's visit by The Duchess to @fosteringnet will celebrate the brilliant work of foster carers in supporting vulnerable young people," tweeted Kensington Palace's newly-created account, later adding: "She's here! The Duchess of Cambridge meets Fostering Network staff before going into a private meeting."
Kate's work with The Fostering Network is designed to help more people get involved in fostering as over 8,600 new foster homes are currently needed.
While Kate doesn't have an official link with The Fostering Network, their work with children and young people is close to her heart.
As Kate left the building, after being praised by president Jim Bond for "shining a light on fostering", she was given a memory box by the charity to remind of her day with them.