Queen Elizabeth II has postponed a meeting of her Privy Council advisory group after doctors advised her to rest, Buckingham Palace said Wednesday, the day after she appointed Liz Truss as Britain's new prime minister.
"After a full day yesterday, Her Majesty has this afternoon accepted doctors' advice to rest," the palace said in a statement.
"This means that the Privy Council meeting that had been due to take place this evening will be rearranged."
The 96-year-old monarch, who is currently on her traditional summer retreat at Balmoral in the Scottish Highlands, has been dogged by problems walking and standing since last year, forcing her to cancel a series of public engagements.
Fears about a flare-up of what royal officials call "episodic mobility problems" prevented her returning to London to accept outgoing leader Boris Johnson's resignation and to appoint Truss on Tuesday.
The elderly sovereign, looking frail and holding a walking stick for support, was seen in an official photograph of the symbolic ceremony shaking hands with Truss as she invited her to lead a new government.
The constitutional role -- the so-called "kissing of the hands" ceremony -- usually takes place at Buckingham Palace in London.
It was the first time it had been held outside London since 1952, when Winston Churchill met the new queen at Heathrow Airport after the death of her father, George VI.
The last time the handover of power took place at Balmoral was in 1885 when Victoria was on the throne.
The current queen also carried out another duty after Tuesday's prime ministerial handover, Britain's Press Association reported.
Wednesday evening's scheduled Privy Council meeting, to be held virtually, would have seen Truss take an oath and new cabinet ministers sworn into their roles, and also admitted new ministers to be privy counsellors if they were not already.
Meetings of the council, a royal advisory body dating back hundreds of years and comprising hundreds of members, including religious and political leaders, usually happen monthly.
Last week, Britain's longest-serving monarch skipped the Highland Games event, a traditional highlight of her summer in Scotland.
The latest cancellations will revive concerns about her health.
She has cut back on public engagements since last October after an unscheduled overnight stay in hospital for an undisclosed condition.
She was also hit by a bout of Covid earlier this year, that she said left her "exhausted".
During her Platinum Jubilee celebrations this summer, the monarch travelled to Buckingham Palace just twice and made only fleeting appearances during the four days of events.