The Queen has been forced to pull out of a service at Paul’s Cathedral at last minute as she is “under the weather”, Buckingham Palace officials have said.
The 92-year-old was due to attend the service to mark the 200th anniversary of the Order of St Michael and St George.
She will instead be represented by the Duke of Kent.
A statement from Buckingham Palace 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.
“Her Majesty will be represented by The Duke of Kent as Grand Master of the Order.”
It is understood that a hospital and doctor is not involved at this stage.
The Queen will still travel from Buckingham Palace to Windsor this afternoon for the weekend as planned.
She is still scheduled to attend a full week of engagements of Scotland next week.
The news comes after the Queen underwent eye surgery to remove a cataract in May.
The monarch has opted to wear sunglasses instead of cancelling a series of public engagements.
She underwent the delicate procedure at the private King Edward VII’s hospital in London, where she was treated as a day patient.
The planned operation resulted in a success.
Piers Morgan sent his best wishes, tweeting: “Her Majesty very rarely pulls a sickie. Hope she’s OK.”
It follows a busy month for the Queen, who enjoyed five days at her favourite week of the month, Royal Ascot.
This week the nation’s longest-serving monarch joined grandson Prince Harry and his wife Meghan Markle at her Young Leaders Awards at Buckingham Palace.
The event honoured young people from the Commonwealth who have strived to improve their communities.
Prince Harry will take over the role of patron of the Young Leaders programme from the Queen next year.
Despite the health issue, the Queen is known to be of robust constitution.
Her son, Prince Andrew the Duke of York, once described his mother as being incredibly fit for her age.
The 92-year-old monarch still rides her Fell ponies at Windsor, and drives, mainly around her private estates.
Her good health allows her to still carry out most of the royal engagements in her agenda.
But the Queen has called time on her overseas travels, leaving long-haul destinations to the younger members of her family.
However she still has a busy diary of events, and in 2017 attended 296 events.
Her son Prince Charles was forced to step in for the Queen to lead the nation in remembering the fallen on Remembrance Sunday at Centopath. It marked the first time the Queen had watched the ceremony from a nearby balcony.
Meanwhile, just before Christmas in 2016 both the Queen and her husband Prince Philip fell ill with heavy colds, forcing them to delay their yearly visit to Sandringham for the day,
The 92-year-old monarch was too unwell to attend the Christmas Day service at St Mary Magdalene church and the New Year’s Dsy service.
She later described it as a “particularly grisly mixture of cold and flu”.
Hollywood star Angelina Jolie was also invited to Thursday’s service as a recipient of an honour from the Order, which is granted by the Queen on the advice of the Prime Minister. It is for distinguished services in connection with foreign affairs and service overseas.
A smiling Ms Jolie, looking elegant in a simple and fitted stone-coloured mid-calf dress with matching gloves and hat, was seen chatting to former Labour Defence Secretary and Nato secretary general Lord Robertson. She was admiring his ceremonial robes.
He attended in his role as chancellor of the order and was part of the main procession along with Sir Jeremy Greenstock, Britain’s former ambassador to the UN.
The cathedral is the home of the Chapel of the Order of St Michael and St George, which was formally dedicated in 1906.