The couple sent cake and coffee to those patiently waiting for the birth of the new royal baby by the famous Lindo Wing.
Kate is due to give birth to the couple's second child any day now, with speculation that she is now past her due date.
John Loughrey, who is patiently waiting for the new arrival, told The Sun: "Two men in dark suits arrived at 9am and said they had cakes and coffee from the Duke and Duchess of Cambridge.
"It's made me quite tearful to know that they care. We're really touched. We're cold and tired and this really cheered us up. I will never forget this for as long as I live."
The Duke and Duchess are already parents to Prince George, who was born in July 2013.
Tomorrow (April 29) will also be the couple's fourth wedding anniversary.
