The Princess of Wales is set to be away from public duties for up to three months to give her time to recover from abdominal surgery.
The Prince of Wales is also stepping temporarily back from official duties while his wife is in hospital and in the immediate aftermath while she recuperates.
And following the news that King Charles will undergo hospital treatment for an enlarged prostate next week, the monarch will also be out of action, meaning that duties will fall on other senior royals.
The King's slimmed down monarchy only has four working royals under the age of 65, the Prince and Princess of Wales and the Duke and Duchess of Edinburgh.
And with William and Kate out of action, extra duties could be expected to fall to Prince Edward and Sophie.
The Edinburghs resumed their royal duties after the Christmas break with Edward visiting a school in Windsor and carrying out a number of engagements across Birmingham and the West Midlands.
Meanwhile, Duchess Sophie enjoyed a hands-on visit to a Battersea-based charity on Tuesday and will tour the Gabrielle 'Coco' Chanel Exhibition at the Victoria and Albert Museum in London.
Other working royals include the Princess Royal, known for her no-nonsense hard-working approach, the Duke and Duchess of Gloucester, and the Duke of Kent, 88, and Princess Alexandra, 87, but the latter two have appeared increasingly frail in recent times.
Alexandra's public outings have lessened in recent years. She carried out three engagements in 2023, including attending King Charles's coronation, visiting the Chelsea Flower Show and presenting medals to members of The Royal Lancers (Queen Elizabeth's Own) in her role as Deputy Colonel-in-Chief.
But despite being the oldest working royal, the Duke of Kent undertook 69 engagements in 2023, according to The Telegraph.
Meanwhile, Princess Anne had already resumed her public duties on 4 January following the festive break.
And she and her husband, Vice Admiral Sir Tim Laurence, were the first royals to undertake an overseas visit to Sri Lanka earlier this month.
Princess Anne is known to also pack a large number of engagements into her days, with as many as four or five.
Following her three-day trip to Sri Lanka last week, the Princess Royal was back to her busy schedule on Tuesday, visiting a number of charities and patronages across Scotland.
The prospect of the King being treated in hospital and the Prince of Wales halting his official duties to care for his wife raises questions over which Counsellors of State might be needed to step in.
In the event a monarch cannot undertake their duties as sovereign on a temporary basis due to illness, two or more Counsellors of State are appointed by Letters Patent to act in their place. Usually the duty would fall to William in the first instance.
Buckingham Palace has said, however, that it did not anticipate Counsellors of State being necessary when the King is treated in hospital for an enlarged, benign prostate next week.
Provisions for the counsellors are made under the Regency Acts 1937 to 1953 and those who can currently stand in for Charles include Queen Camilla, and the four most senior adults in the line of succession over the age of 21, the Prince of Wales, the Duke of Sussex, the Duke of York and Princess Beatrice.
But in 2022, the King asked Parliament to add his youngest brother the Duke of Edinburgh and sister the Princess Royal as extra Counsellors of State so they can deputise for him if need be, and the addition was fast-tracked into law.
There has been calls from royal watchers for Princess Beatrice and Princess Eugenie to become full-time working royals. However the York sisters have carved out their own full-time careers since graduating from university.
Beatrice, 35, is Vice President of partnerships and strategy for Afiniti technology, while Eugenie, 33, is a director at Hauser & Wirth art gallery.
The Princesses have been attending events at the World Economic Forum in Davos this week, with Eugenie giving a talk in support of her charity, The Anti-Slavery Collective.
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