The Queen has been forced to cancel a planned visit to Wales after suffering from symptoms of gastroenteritis, Buckingham Palace said.
The 86-year-old monarch was due to attend a military celebration in Swansea tomorrow during the city's St David's Day celebrations.
A palace spokeswoman said the Queen will instead spend the weekend at Windsor and will be assessed in the coming days.
Queen Elizabeth was due to attend a military service in the city, but her duties will now be carried out by the Lord Lieutenant of West Glamorgan, Byron Lewis.
The BBC reported that the ceremony was due to be the first time that the Queen was to present leeks to 3 Royal Welsh, which is the reserve force of the regiment.
The ceremonial presentation of leeks dates back to at least 1916 and Welsh Guards at the Somme in World War I.
Gastroenteritis is an infection of the stomach and bowel, and the most common symptoms are vomiting and repeated episodes of diarrhoea.
The Queen presented a host of Olympic stars with honours during an investiture ceremony at Buckingham Palace on Thursday.
She and the Duke of Edinburgh are due to fly out to Rome for a two-day visit next week.
A palace spokesman said the Queen's visit to Rome was still due to take place but a decision would be made after she is assessed in the coming days.Suggest a correction