Since her coronation in 1952, when Winston Churchill was PM, she has witnessed no fewer than 14 different people in the role.
Here are the British PMs she has seen during her time as monarch.
Winston Churchill (1951-1955)
Churchill was already in his second spell as prime minister when Elizabeth ascended the throne.
He had served under her father twice, firstly between 1940 and 1945 when leading the country during the Second World War.
Anthony Eden (1955-1957)
Eden's handling of the Suez Crisis would later contribute to his ranking as one of the worst British leaders of the 20th Century but the Queen was said to have found him a sympathetic listener to her concerns.
Harold Macmillan (1957-1963)
Following Eden’s resignation, Macmillan was picked to be the next prime minister by the Queen herself, after taking advice from Winston Churchill.
Macmillan, a Conservative, reportedly told the Queen he couldn’t guarantee his government would last six weeks due to the fallout of the Suez Crisis, though he went on to be prime minister for six years.
He reportedly called the Queen "a great support, because she is the one person you can talk to".
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Sir Alec Douglas-Home (1963-1964)
Like Macmillan, Douglas-Home was picked to be prime minister by the Queen, who already knew him as he was a childhood friend of the Queen Mother's.
However, he was only PM for two days short of a year, as the public had lost faith with the Conservatives following the Profumo affair.
Harold Wilson (1964-1970 and 1974-1976)
Wilson was the Queen's first Labour Prime Minister and served two separate stints as PM.
The pair were said to have had a relaxed relationship - he described his visits as like “going to see mother”, and he even helped out with the dishes after royal barbecues.
Wilson was one of only two prime ministers whose resignation dinner was attended by the Queen - the other being Churchill.
Sir Edward Heath (1970-1974)
The Queen and Sir Edward Heath reportedly had a strained relationship at times because of their differences over European integration.
Years later, Heath famously fell asleep in front of the monarch during a dinner at Downing Street hosted by then-prime minister John Major.
James Callaghan (1976-1979)
The pair had a warm relationship and on one occasion, the Queen apparently placed a flower in his buttonhole during a stroll around Buckingham Palace.
But Callaghan also knew the score, reportedly saying: "What one gets is friendliness but not friendship".
Margaret Thatcher (1979-1990)
The topic of the Queen's relationship with Margaret Thatcher is regularly up for grabs and was said to be one of the frostiest relationships between the monarch and any of her prime ministers.
But Thatcher, who was just six months older than the Queen, later wrote: "Stories of clashes between ‘two powerful women’ were just too good not to make up".
Despite the reports the Queen attended Thatcher’s funeral in 2013. It was only the second time she had attended the funeral of a former prime minister.
Sir John Major (1990-1997)
Of their weekly briefings, the Tory PM said: "We would sit down and we would talk about whatever was relevant.
"There’s nobody else ever there. The only other living soul present is often the Queen’s corgis, they tend to amass around the chair."
Tony Blair (1997-2007)
Tony Blair was reportedly the first prime minister to move the day of the weekly meetings with the Queen so he could prepare for PMQs.
He was known to occasionally mess up Royal protocol, including revealing to an audience what the monarch had said to him in one of their confidential meetings - a big no-no.
Gordon Brown (2007-2010)
The Queen is said to have had a polite working relationship with Gordon Brown, who was perhaps easier to work with than his predecessor.
On one occasion she jokingly imitated his Scottish accent, and for their final meeting after his resignation, the Queen reportedly invited his family along.
David Cameron (2010-2016)
As the Queen's fifth cousin, twice removed, David Cameron is actually related to the monarch, and also the youngest prime minister during her reign.
He, too, broke royal protocol by telling former New York mayor Michael Bloomberg that the Queen had "purred down the line" when he informed her that Scotland had voted against independence - something he later apologised for.
Theresa May (2016-2019)
The Queen was reportedly frustrated that May did not tell her of her plans for Brexit shortly after she became prime minister.
However, a royal butler told a newspaper the pair had a "bond" together, saying "they get on really well".
Boris Johnson (2019-today)
Boris Johnson is another PM found to be distantly related to the Royal family, according to a BBC’s ‘Who Do You Think You Are?’ programme in 2008.
During his war of words with Dominic Cummings since his departure from Number 10, Cummings claimed he had to stop the PM from attending his weekly meeting with the Queen in person in March 2020, warning him he could kill the monarch.
So.. which one was her favourite?
It's hard to be sure. Asked once to name her favourite PM, she replied: "Winston [Churchill] of course, because it was always such fun."
The monarch attended Churchill's resignation dinner. But she did the same for Harold Wilson, suggesting he was a favourite too.
The Queen was also said to have got on "really well" with Theresa May.
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Can Queen Elizabeth overrule the prime minister?
The Queen is constitutionally empowered to exercise the royal prerogative against the advice of the prime minister or the cabinet, but in reality would only do so in emergencies.
She also has 'reserve powers' that allow the appointment and dismissal of them.
Watch: The Queen still drinks alcohol