The 92-year-old was set to attend a special church service to mark the bicentenary of an order of chivalry but was feeling “under the weather,” a Buckingham Palace spokeswoman said.
“The Queen is feeling under the weather today and has decided not to attend this morning’s service at St. Paul’s Cathedral marking the 200th anniversary of the Order of St. Michael and St. George,” the palace said in a statement. “Her Majesty will be represented by [her cousin] The Duke of Kent as Grand Master of the Order.”
There is no cause for alarm, though, as royal sources point out to PEOPLE that a doctor has not been called. The Queen is also still scheduled to travel to Windsor Castle later on Thursday.
Only two nights ago, she was in good spirits alongside grandson Prince Harry and Meghan Markle, the Duke and Duchess of Sussex, as they celebrated young leaders from around the world at a Buckingham Palace party.
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She also spent last Sunday in the sunshine at a polo match with her husband of 70 years, Prince Philip. Earlier this month, it was revealed she had quietly undergone surgery to remove a cataract — leading to her wearing sunglasses in public.
The news came as Prince William jetted home after a successful five-day tour to Jordan, Israel and the disputed territories.