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.