Donald Trump visited the Queen on Tuesday night as Buckingham Palace hosted the Nato summit.
The US President and other Nato leaders took part in a formal reception at the Queen’s London residence attended by public figures including Jeremy Corbyn and Boris Johnson.
Outside, hundreds of people, including scores of nurses and doctors, descended on the gates of the famous building to protest Mr Trump’s visit and his controversial comments about the NHS.
The Queen, the Prince of Wales and the Duchess of Cornwall formally greeted the Nato leaders at the reception, which was held to coincide with the 70 year anniversary of the alliance.
Other royals including the Duchess of Cambridge, the Earl of Wessex, and the Princess Royal, were also in attendance.
Prior to the reception at the Palace, the President was also given a warm welcome by Prince Charles and the Duchess of Cornwall at Clarence House.
Earlier on Tuesday, Mr Trump met Nato secretary general Jens Stoltenberg at Winfield House in Regent’s Park in London.
During a press conference following the meeting Mr Trump attacked France’s Emmanuel Macron, Barack Obama and the Democrats.
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When asked about the upcoming British election, he claimed he was not getting involved, saying “I don’t want to complicate it”, before boasting of all the US electoral candidates he had helped win seats in midterm elections.
The president also denied claims the US was eyeing up the NHS, saying “we wouldn’t want it even if it was offered to us on a silver platter”.
When asked about Labour leader Jeremy Corbyn, he said: “I can work with him. I’m a very easy man to work with.”
The president also used the time to criticise French president Mr Macron for his claim Nato is “brain dead” and to attack the current impeachment proceedings against him.
The two men met later at the US ambassador’s residence in London, Mr Trump acknowledged the need for greater “flexibility” in the way in which Nato responded to global threats.
Mr Macron in turn accepted the US had “over-invested” in the alliance for “decade after decade” – a long-standing gripe of the US leader.
The meeting of Nato leaders is being held to mark the alliance’s 70th anniversary.
Prime Minister Boris Johnson hosted talks with Mr Macron, Turkish President Recep Tayyip Erdogan and German Chancellor Angela Merkel ahead of the main gathering in an attempt to iron out some of the differences between them.
The main Nato talks will take place on Wednesday at The Grove, a country house hotel near Watford.
The meeting is expected to consider new threats, including in the areas of cyber and space, after the alliance last month declared space one of its operational domains alongside air, land, sea and cyber.