The Queen has been forced to cancel a visit to an official engagement in Wales after falling ill with gastroenteritis.
She was due to attend a military parade in Swansea on Saturday 2 March, as part of the St David's Day celebrations.
A palace spokeswoman said: "She will be assessed in the coming days. Her Majesty is currently spending the weekend at Windsor, as usual."
The monarch, who is 86, was scheduled to present the 3rd battalion The Royal Welsh Regiment with a ceremonial leek as part of the parade. The leek is one of the national symbols of Wales.
She was also to meet soldiers and their families before having lunch at the George Hall as part of the three-hour long engagement.
The palace spokeswoman said: "The Queen will no longer visit Swansea as she is experiencing symptoms of gastroenteritis. She will be assessed in the coming days.
"Her Majesty is currently spending the weekend at Windsor, as usual."
The ceremony will go ahead as planned, with the Lord Lieutenant of West Glamorgan, Byron Lewis, making the presentation on her behalf.
The Queen performed her duties as usual on Thursday, presenting Olympic stars with honours in an Investiture ceremony, and is still scheduled to fly to Rome for a two-day visit next week.
Gastroenteritis is a stomach illness often caught through food poisoning or the norovirus. Symptoms include vomiting, diarrhoea and dehydration.
Last December the Queen missed a Sunday church service at Sandringham after falling ill with a cold, and was forced to cancel a public appearance in October and another church visit due to back problems.
Her husband Prince Philip, who is 91, fell ill last June with a bladder infection, which may have been caused by standing in the cold for hours on a barge on the Thames during the Diamond Jubilee celebrations.
He was taken to hospital hours before the closing ceremony of the celebrations, and also missed a number of other public appearances, including a thanksgiving ceremony at St Paul's Cathedral.