The Queen's diary is 'under review' and she is unlikely to return to attending certain major public engagements again, according to reports.
Sources claimed the monarch, 95, is not ill and is committed to her duties.
However senior royal aides are understood to have accepted that the "frailties that come with living a long life" are finally catching up with her.
A source told the paper: "The Queen is still as alert, able and interested as ever but, physically, she isn't as strong as she once was, which is entirely understandable for a woman of her age". reports the Mail.
It comes after confirmation the royal family will attend the annual Commonwealth Day service, but the Queen will miss the event for the first time in almost a decade.
The Queen, who has recently recovered from a bout of Covid, had hoped to attend the important event in the royal calendar alongside the Prince of Wales, Duchess of Cornwall and Duke and Duchess of Cambridge.
The Commonwealth, affectionately known as the "family of nations", has played an important role throughout her reign, and she takes a special interest in the institution.
But on Friday a Buckingham Palace spokesman said: "After discussing the arrangements with the royal household, the Queen has asked the Prince of Wales to represent Her Majesty at the Commonwealth service at Westminster Abbey on Monday.
"The Queen will continue with other planned engagements, including in-person audiences, in the week ahead."
She last missed the service nine years ago, in 2013, while recovering from a nasty bout of gastroenteritis.
Before that, the Queen had not been absent from a Commonwealth Day observance service for 20 years, the last time being when she had flu in 1993.
Highlights of the service at Westminster Abbey will include an address by former archbishop Lord Sentamu, a reflection by young Tongan leader Elizabeth Kite and special musical performances from Emeli Sande and Mica Paris.
Organised by the Royal Commonwealth Society, the service will feature the Queen's Commonwealth Day message. The service would have been the Queen's first major public appearance since reaching her Platinum Jubilee milestone in February.
Her decision not to attend is likely to be interpreted as a precautionary measure by royal commentators, and a practical move, rather than a new health issue.
With the Queen due to celebrate her 96th birthday in less than six weeks, maintaining her comfort is a consideration and it is understood she has been pacing herself, although she was keen to do what work she could during her bout of Covid.
Commonwealth Day has not been celebrated in person since 2020, when the Duke and Duchess of Sussex made their last public appearance with senior members of the royal family before moving to North America.
