Mr Johnson is still married to second wife Marina Wheeler but he and Ms Wheeler announced they were in the process of divorcing in September 2018. Carrie Symonds has been the Prime Minister’s partner since last year. A source told The Sun: “Most women of the Queen’s generation simply wouldn’t want an unmarried couple staying with them and sharing a bedroom and she is no different, so it was totally inappropriate of Boris.
“What was perhaps more troubling for the Queen was that he turned up with an unmarried woman who’s young enough to be his daughter.”
Mr Johnson is 55 and Miss Symonds is 31.
The source continued: “The Queen is the head of the Church of England.
“She felt uncomfortable about it.
The Queen felt 'uncomfortable' about unmarried Carrie Symonds and Boris Johnson spending the night
Mr Johnson is separated from his second wife Marina Wheeler
“It’s just not something she approves of.”
Prime Ministers typically spend the weekend at Balmoral in autumn but Mr Johnson cut his trip to just one night and returned to London on the Saturday morning to deal with Brexit.
The Palace declined to comment.
Mr Johnson married Ms Wheeler in 1993, the same year he divorced his first wife Allegra Mostyn-Owen.
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Edward Heath was the last unmarried Prime Minister
The couple separated last year.
The last unmarried Prime Minister before Mr Johnson was Edward Heath who was a bachelor.
Balmoral is located in Aberdeenshire.
It is the private property of the royal family and not part of the crown estate.
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Balmoral Castle in 1964
Holyrood House is the Queen's official Scottish residence
Prince Albert purchased the estate in 1852 for his wife, Queen Victoria.
In 1887, Victoria’s daughter Princess Beatrice gave birth to Victoria Eugenie of Battenberg at Balmoral.
Victoria Eugenie would marry King Alfonso XIII of Spain in 1906 and would become Queen consort of Spain.
A map of royal residences
Other royal residencies in Scotland include Palace of Holyrood House, the Queen’s official residence in Scotland.
There is also Birchall, the Scottish residence of Charles, Prince of Wales.
Charles inherited the property in 2002 from his grandmother Queen Elizabeth the Queen Mother upon her death.
The Queen invited Mr Johnson to form a Government in July
Albert also bought Birchall in 1849 and gave it to his eldest son the future King Edward VII.
Holyrood Palace was the primary seat of the Scottish royal court until 1603 when King James VI of Scotland also became King James I of England.
During the reign of King George V it underwent refurbishment and was designated the monarch’s official residence in Scotland.