Prince William's pregnant wife Catherine was given a badge to help expectant mothers get a seat on London's Underground when she accompanied Queen Elizabeth II on a visit Wednesday to mark the train network's 150th anniversary.
The queen, who was fulfilling her first public engagement for more than a week after suffering symptoms of gastroenteritis -- an infection of the stomach and bowel -- smiled broadly during the visit to Baker Street station.
Catherine, 31, was presented with a "Baby on board" badge by London Underground chief operating officer Howard Collins.
She held it against her teal-coloured coat and joked "I'll make sure I wear it at home."
The Underground gives the badges out to pregnant women to let other passengers know they may need a seat.
Now five months pregnant, Kate still has a slim figure but her baby bump is growing by the week.
Collins said afterwards: "Kate said 'Oh yes, I've seen this before.' She used to travel on the Tube so she probably saw them then.
"She asked me 'How do they work?' and I said they're fantastic, they really do make a difference -- saves men the embarrassment of having to guess if a woman is pregnant."
The 86-year-old queen's illness forced her to be admitted to hospital on March 3 for the first time in a decade. She and her husband Prince Philip had to cancel a planned visit to Rome a few days later.