A-list stars are no strangers to public transport. When Rihanna performed at London's O2 she relied on the Jubilee Line to get her there on time (rookie error) and Katie Holmes, Bradley Cooper, Anne Hathaway and Jay-Z are all regular passengers on New York's Subway system. But the last person we expected to see topping up her Oyster Card is the Duchess of Cambridge.

However, this morning five-months pregnant Kate joined the Queen and the Duke of Edinburgh at Baker Street tube station to mark the 150th anniversary of the London Underground. Wearing a teal By Malene Birger coat, black Cornelia James gloves and her Episode Angel suede pumps (the second time she's worn them this week), it's fair to say that the glamorous mum-to-be is not your average stressed out and sweaty commuter.

Along with a black hat and sapphire earrings, Kate's hair was styled in loose curls showcasing the textures and tones of her tresses. The overall look reminded us of an outfit she wore back in March 2012 on a trip to Leicester.

Kate demonstrated her sense of humour when she met London transport staff and was handed a 'Baby On Board' badge, regularly spotted on pregnant travellers. She laughed and said "I'll make sure I wear it at home."

Watch the video of the Kate on the London Underground

This Duchess is on somewhat of a style roll after visiting the charity Child Bereavement UK yesterday wearing a monochrome Contrast Collar Dress from Topshop and 'Redgrave coat' from cashmere designer Goat. She experimented with Peter Pan collar featured on the frock, which she is believed to have picked up on a recent shopping trip to the high street stalwart. That's two new coats and a new dress so far this week by our count - could it be that the brunette and her bump have invested in a whole new pregnancy wardrobe? Watch this space!

For more looks from the Duchess, take a look through Grazia's Kate Middleton Look Book below.