Queen Elizabeth II has “reluctantly” taken the advice of medical professionals who have instructed the 95-year-old to rest for the next few days.
The British monarch was scheduled to travel to Northern Ireland on Wednesday for a two-day visit and is said to be “disappointed” that the trip will no longer go ahead as planned.
Instead, the head of state will be retiring to Windsor Castle, where on Tuesday she welcomed political figures and tech industry leaders, including Bill Gates, for a post-summit reception.
Buckingham Palace said in a statement: “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, whose husband, Prince Philip, died on April 9, recently raised concerns over her health after making a public appearance last week in Wales with a walking stick for the first time in nearly 20 years.
The nation's longest-reigning monarch had only previously been seen using a walking aid following knee surgery to remove a torn cartilage in her right knee back in 2003.
Over the weekend, the Queen attended horse races at Ascot Racecourse, where she arrived without the medical aid.
The Queen is next scheduled to make an appearance in Glasgow for the Cop26 UN climate change conference, which will take place at the end of October.