The Queen has cancelled a trip to Northern Ireland and has "reluctantly accepted medical advice to rest for the next few days", Buckingham Palace said.
The 95-year-old monarch is said to be in good spirits but disappointed not to be able to carry out the two-day trip, which was due to begin on Wednesday.
The Queen has had a busy few days and hosted a major Global Investment summit at Windsor Castle on Tuesday evening.
A Buckingham Palace spokesman said: "The Queen 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 today and tomorrow.
"The Queen sends her warmest good wishes to the people of Northern Ireland and looks forward to visiting in the future."
The Queen's decision is understood not to be related to coronavirus.
