The 96-year-old monarch’s latest setback could raise concerns for her health the day after she was pictured in an audience with Liz Truss, as she appointed her as the United Kingdom’s new prime minister.

“After a full day yesterday, Her Majesty has this afternoon accepted doctors’ advice to rest,” a palace spokesman said.

“This means that the Privy Council meeting that had been due to take place this evening will be rearranged.”

The Queen remains at Balmoral Castle in Aberdeenshire and the latest advice does not involve a hospital stay.

The monarch has ongoing mobility issues and had been due to hold the Privy Council virtually on Wednesday.

During the proceedings, Truss would have taken her oath as First Lord of the Treasury and new cabinet ministers would have been sworn into their roles, and also made privy counsellors if not already appointed as one in past.

There is no constitutional issue with the delay to the proceedings, the palace said.

The smiling head of state looked bright but frail and used a walking stick during Tuesday’s audience, which followed a visit from outgoing prime minister Boris Johnson as he tendered his resignation.

It was the first time in her 70-year reign that the Queen has appointed a prime minister at Balmoral.

The two politicians made the trip from London rather than making the monarch, who has suffered episodic mobility problems since last October, travel back from Scotland.

The Queen is on her summer break on the Balmoral estate and not due to return until early October.

With her hair neatly curled, the Queen, dressed in a blouse, cardigan and a Balmoral tartan skirt, stood as she met Truss.

The Sun reported recently that the Prince Charles had been making regular morning visits to see his mother as she continues to struggle with her mobility, with the unplanned visits considered highly unusual.

She missed the Braemar Gathering highland games last weekend, which she usually attends each year.

Buckingham Palace has declined to give an ongoing commentary on the monarch’s health.

During her Platinum Jubilee celebrations, the Queen only travelled to Buckingham Palace twice, first for her Trooping the Colour balcony appearance and then for a finale after the pageant.

She spends most of her time at Windsor Castle, 35km from central London, living there during the pandemic and while major renovations take place at the Palace, and for her comfort.

She secretly spent a night in hospital in October undergoing tests and was then under doctors’ orders to rest for the next three months, missing the Remembrance Sunday Cenotaph service and COP26 climate change talks.

The Queen caught COVID-19 in February and suffered from mild cold-like symptoms but said the virus left her “very tired and exhausted”.