Kate Middleton Gets "Baby on Board" Button, Pregnancy Curves Concealed With Long Blue Coat at London

Britain's Catherine, Duchess of Cambridge, arrives at Bakerloo tube station in central London on March 20, 2013 for a public engagement with Britain's Queen Elizabeth II and Prince Philip, Duke of Edinburgh. Credit: ANDREW COWIE/AFP/Getty Images

The Duchess of Cambridge is getting some wonderful swag in honor of her baby-to-be! Visiting London's Baker Street Underground along with grandparents-in-law Queen Elizabeth and Prince Phillip, pregnant Kate Middleton was gifted with a "Baby on Board" button from the staff. "I'll make sure to wear it at home!" the 31-year-old royal said, laughing.

Concealing her pregnancy curves in a blue Malene Birger coat, Middleton and the Queen, 86, were on hand for the unveiling of a brand-new subway train, named the Queen Elizabeth II. Common-born Middleton once rode "the tube" daily when she worked at clothing retailer Jigsaw. "I used to travel on the tube on a regular basis," remarked the royal mom-to-be. "I miss travelling on the Tube." (The London Tube also celebrates its 150th anniversary this year.)

The event was the Queen and Duchess' third joint engagement -- sans Prince William -- together. Clad in a summer tweed coat by Karl Ludwig, the Queen chose the unveiling for her first major engagement since her hospitalization with gastroenteritis, which landed her in the hospital earlier this month.