Queen to receive new UK prime minister at Scottish retreat
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It will be the first so-called "kissing of the hands" ceremony to take place away from central London since Winston Churchill met the queen at Heathrow Airport in 1952 after she came to the throne.
Foreign Secretary Liz Truss is favourite to win the nomination from Conservative party members, after Johnson announced he would quit in July after a series of scandals.
The winner of the contest is due to be announced on Monday.
The queen is on her traditional summer break in the Scottish Highlands, which usually lasts until October.
She was due to return to London to carry out the ceremony.
However, she has been dogged by mobility problems since October, when she required an overnight stay in hospital for an unspecified condition.
On medical advice, she has since cut back drastically on her public appearances, and has complained of difficulties standing and walking.
She admitted to being left "exhausted" by a bout of Covid earlier this year, and on the rare occasions she has been seen, has walked with a stick.
At the Chelsea Flower Show, she toured the site in a motorised golf cart.
The queen made two appearances at four days of public celebrations to mark her record-breaking 70 years on the throne in early June.
But even then, the effort forced her to sit out a church service commemorating her reign and a star-studded pop concert outside Buckingham Palace.
She managed though to make a final balcony appearance with her immediate successors -- Prince Charles, his son William and grandson George.
Her Balmoral trip came after reports that she has had a stairlift installed at the private estate.
Earlier this month, she cancelled her traditional official "Welcome to Balmoral" and instead hosted a small private event.