There have been 13 American presidents in power during the Queen’s reign so far.
Following Donald Trump’s visit to Windsor Castle on Friday, the monarch will have met all of them – except one.
Lyndon B Johnson, who took over in 1963 following John F Kennedy’s assassination, never crossed paths with the Queen.
Elizabeth II has played a pivotal role over the decades in the UK’s relationship with the leaders of one of its closest allies.
Harry S Truman
In 1951, a young Princess Elizabeth – unknowingly three months away from becoming queen – travelled to Washington and saw President Harry S Truman, who was still in the Oval Office when she acceded to the throne.
Dwight D Eisenhower
During her first state visit to America in 1957, now a Queen, she met Dwight D Eisenhower.
They met again in Canada in 1959 and travelled on the Royal Yacht Britannia together.
The Queen was said to have had an affectionate relationship with Mr Eisenhower, who was even invited to stay at the Queen’s Scottish hideaway Balmoral Castle.
John F Kennedy
The glamorous JFK and his wife Jackie dined with the Queen and the Duke of Edinburgh at Buckingham Palace in June 1961.
Lyndon B Johnson
Mr Johnson, then vice-president, took over after Mr Kennedy’s assassination in 1963.
He was president until 1969 – but the Queen never met him, and he died in 1973.
Richard Nixon dined with the Queen at Buckingham Palace in February 1969.
The Queen also met Mr Nixon at Chequers in October 1970 and was photographed with him outside the prime minister’s official country residence.
In 1976, during the US bicentennial, the Queen met Gerald Ford in the US.
In 1977, the monarch was pictured in a billowing, wide-sleeved yellow gown alongside Jimmy Carter, in a black tie and tuxedo, when he came to London.
Ronald and Nancy Reagan stayed at the Queen’s favourite home Windsor Castle in 1982.
The monarch and the former film star shared a bond through their love of horses and rode side by side in Windsor Great Park.
Both looked relaxed and informal in jodhpurs and riding boots, with the Queen dressed down in her headscarf.
She also met Mr Reagan during an official visit to America’s West Coast in 1983.
George Bush Snr
George Bush Snr had lunch with the Queen at Buckingham Palace in 1989.
She also visited him in the US in 1991 – the trip that led to “Podiumgate” – when all that could be seen of the Queen above the lectern when she was delivering an address on the White House lawn was her hat.
Bill Clinton and his wife Hillary met the Queen several times, including in December 2000 when, along with daughter Chelsea, they dropped in on the Palace.
George W Bush
George W Bush visited the head of state at the Palace in July 2001.
Two years later in November 2003, Mr Bush paid an official state visit – the first by a US leader – and the Queen gave him a wide smile as they shook hands at her London residence.
When the Queen encountered Mr Bush again in Washington DC in 2007, the president winked at her after making a gaffe.
At a welcome ceremony on the south lawn of the White House, he mixed up his dates in a speech – almost ageing the Queen by 200 years.
Turning to the Queen and winking, he joked to his audience: “She gave me a look that only a mother could give a child.”
Mr Bush – in 2008 – was also received by the Queen at Windsor Castle.
The Queen’s relationship with Barack Obama was a warm and friendly one.
They hit it off after a reception ahead of the G20 summit in 2009.
The Queen and first lady Michelle Obama acted like old friends when they put their arms around each other at the end of the event.
A successful state visit to the UK followed in 2011 and the Obamas forged a strong bond with the Queen and her wider family – particularly Prince Harry, now the Duke of Sussex, and the Duke and Duchess of Cambridge.
The Obamas even dropped in to see the Queen the day after her 90th birthday.
The Duke of Edinburgh, then 94, drove the couple the short distance to Windsor Castle after their Marine One presidential helicopter touched down on the manicured lawns of the royal residence.
The Obamas also met Prince George, who was ready for bed in his dressing gown, ahead of dinner with William, Kate and Harry at Kensington Palace.
Mr Trump will be accorded a guard of honour at Windsor Castle and also have tea with the Queen on Friday.
But this will not be a state visit – an offer extended to Mr Trump by Prime Minister Theresa May in the early days of his presidency.
There will be no carriage procession and no opulent state dinner, and, as such, no other members of the royal family will call in to meet the controversial billionaire-turned-politician.