The iconic supermodel was surrounded by photographers as she made her way to a restaurant in the capital on Thursday afternoon (16 January).
Kate's hubby kept a protective arm around her as they made their way into 34 restaurant in Mayfair, where pals including Sadie Frost and Nick Grimshaw had gathered to celebrate her milestone day.
Other celebrity guests at the private event included Stella McCartney, John Galliano, Jo Wood and Topshop owner Sir Philip Green.
Kate's low-key lunch for friends and family surprised many as it had been rumoured that the Croydon-born star - who is mum to daughter Lila, born in 2002 - was planning to jet to Necker Island for the big day.
According to the Sunday Mirror, the model had been offered the use of the idyliic private island by its owner Sir Richard Branson, and was attracted to the idea she could celebrate in private.
All day, presents have been arriving at the star's home in London including a gift bag from Hermes and so many flowers she could probably open her own flower store.
Lucky for some!