Five-months-pregnant Kate was seen in the Sloane Square store on Wednesday, checking out the Seraphine maternity concession.
An onlooker claims a £39 Brooke Butterfly sleeve dress from the range caught the eye of the Royal mum-to-be.
Kate is known for her love of combining high street finds with high-end designer labels – just last week she caused a stir in TopShop when she was spotted perusing the rails by fellow shoppers, and on her recent 'Royal Away Day' engagement in Grimsby, she sported a dress from high street retailer Phase Eight and a coat from Hobbs.
Seraphine maternity wear has been popular with other famous mums, including Kate Hudson, Halle Berry and Emma Bunton.
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