The Queen has "reluctantly accepted medical advice to rest for the next few days" and will not be travelling to Northern Ireland today, Buckingham Palace has said.
"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 palace statement added.
"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.