The Queen had to miss a public engagement after suffering a nosebleed, Buckingham Palace has confirmed.
She was due to attend a service of the Royal Victorian Order at Windsor Castle with other senior members of the Royal Family on Wednesday morning, but was forced to pull out.
However, the monarch, who celebrates her 85th birthday next week, recovered enough to attend a reception in the state apartments of the castle afterwards.
It is thought to be the first time she has missed a key public engagement in five years.
A Buckingham Palace spokesman said: "There was a service and a reception at Windsor. She was able to attend the reception but not the service because of a nosebleed."
The Queen has rarely taken time off due to illness during her 59-year reign.
In 2006, she cancelled engagements after straining a back muscle and had official appointments scaled down after she underwent knee surgery in 2003.
As well as the royal wedding later this month, the sovereign's diary for the rest of the year includes a state visit to Ireland next month and US president Barack Obama's visit to Britain.