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
Barack Obama has delighted the crowds at St Andrew's golf course as he teed off his visit to Scotland with a game of golf.
Britain's most senior counter-terrorism officer said "immense" progress had been made in the investigation into the Manchester bombing.
Scotland sees the best of today's weather but temperatures are a good 10C above average for the time of year across much of the UK.