Donald Trump’s state visit to the UK is only the third by a US president.
The Queen has met 12 of the 13 American leaders who have been in office during her reign.
But just George W Bush, Barack Obama and now Mr Trump have been treated to a grand state visit.
Mr Bush’s stay in 2003, while Tony Blair was prime minister, was highly controversial.
Tens of thousands of people came out to protest against the American leader and the war in Iraq, amid unprecedented security for a state visit.
Demonstrations throughout Mr Bush’s stay were mostly peaceful, and peaked with the toppling of an effigy of Mr Bush in Trafalgar Square, which parodied scenes of the capture of Baghdad.
Stop The War Coalition said some 200,000 joined the demonstration.
One protester threw an egg at the presidential cavalcade, but missed.
The Queen told Mr Bush that Britain and America stood firm in their determination to defeat terrorism.
Speaking at a Buckingham Palace state banquet in his honour, she said the two countries had never been closer.
She said of Mr Bush: “The leadership you showed in the aftermath of the terrible events of September 11, 2001 won the admiration of everyone in the United Kingdom.”
The day of the visit began with the Daily Mirror revealing a serious breach of royal security.
Undercover reporter Ryan Parry had posed as a footman at Buckingham Palace for two months, using bogus references to get a job while police and royal staff were preparing for Mr Bush’s stay.
Parry was due to serve breakfast to President Bush’s top aides.
He took pictures inside the palace including of the bed in the Belgian Suite where the president and his wife Laura were due to stay, and of the Queen’s breakfast table.
Both Mr Bush and Mr Obama stayed with the Queen at the palace, but Mr Trump is not residing with the monarch.
Buckingham Palace said this was due to the East Wing of the royal residence being closed due to ongoing building work.
Mr Obama and First Lady Michelle Obama’s state visit in May 2011 came just weeks after the Duke and Duchess of Cambridge’s grand royal wedding.
It was free of the controversy and protests sparked by Mr Bush’s stay.
The Obamas did not attend the Cambridges’ wedding, but their invite to the UK soon after was seen as a sweetener instead.
Newlyweds William and Kate – who had just returned from their honeymoon – travelled to the palace especially to meet the couple on what was the duchess’s first royal duty as a member of the Windsors.
The Queen hailed the US as Britain’s “most important ally” at the banquet and said the historic relationship was “tried, tested and yes – special”.
Mr Obama paid tribute to the monarch and described the two countries’ partnership as being based on a “rock solid foundation built during Queen Elizabeth’s lifetime of extraordinary service to her nation and to the world”.
Actor Tom Hanks, actress Helena Bonham-Carter and director Tim Burton added some Hollywood glitz to the VIPs attending the lavish white-tie affair.
Earlier in the day, Mr Obama and then prime minister David Cameron had teamed up to play table tennis against a pair of 16-year-olds at a south London school, but lost to the teenagers.
The next day Mr Obama addressed both Houses of Parliament at the 900-year-old Westminster Hall, where he declared that both countries “stand squarely on the side of those who long to be free”.
Mr Bush was due to address both Houses in 2003 but this was cancelled due to anti-war protests.
Mr Trump is not addressing Parliament.
Commons Speaker John Bercow insisted in 2017 that Mr Trump should not be allowed to do so because of MPs’ “opposition to racism and to sexism”.