Queen Elizabeth II has cancelled a planned trip to Northern Ireland on medical grounds, Buckingham Palace said on Wednesday.
Royal officials said in a statement that the 95-year-old monarch "has reluctantly accepted medical advice to rest for the next few days".
"Her Majesty is in good spirits and is disappointed that she will no longer be able to visit Northern Ireland, where she had been due to undertake a series of engagements" on Thursday and Friday, the Palace said.
"The Queen sends her warmest good wishes to the people of Northern Ireland, and looks forward to visiting in the future."
A church service to mark the 100th anniversary of the creation of Northern Ireland is due to take place in border Armagh on Thursday.
The Queen, Britain's longest-serving monarch, on Tuesday hosted a reception at Windsor Castle for international business leaders attending a government investment summit.
She also received the Japanese and EU ambassadors via videolink.
Last week, she was seen for the first time using a walking stick in public.
Watch latest videos by DH here: