Queen Elizabeth II will attend her first public engagement for more than a week on Wednesday when she joins Prince William's wife Catherine on a visit to London's Tube network.
The 86-year-old had to cancel a number of events last week as she was still recovering from a bout of gastroenteritis which saw her admitted to hospital on March 3 for the first time in ten years.
Aides said she was continuing her "usual rhythm of business" at Buckingham Palace but the monarch has not attended a public engagement since signing a new Commonwealth charter on March 11.
On Wednesday, the queen will be joined by her husband Prince Philip and Kate, the pregnant wife of her grandson William, on a visit to Baker Street Underground station.
They will mark the 150th anniversary of the Tube by meeting station staff in the ticket hall and then maintenance and train workers down on the platform.