The Queen and Duke of Edinburgh will travel with the Duchess of Cambridge today to Baker Street Underground station in London to mark the transport network's 150th anniversary.
The Queen, who had been suffering symptoms of gastroenteritis, has been carrying out her duties within Buckingham Palace but last week cancelled a trip to London's East End to visit Tech City.
The Duke of York, who carried out the engagement without his mother, said she was "not ill" but stayed at home as precaution.
The last time she was seen at an official event was an engagement last Monday evening when she signed the Commonwealth's new charter.
More top news
Ed Miliband's pitch to business is based on staying in Europe - will this be enough to get their votes?
The DJ involved in a prank that led to the suicide of a nurse said that she thought her inability to have children was 'karma'.
Who's in charge and what happens if there's an international crisis? Here are answers to key questions about the dissolution of parliament.