Donald Trump inspected a Guard of Honour by Grenadier Guards personnel at Buckingham Palace (Picture: MOD).
The US President has began his official three-day state trip to the UK by visiting Buckingham Palace.
The trip includes engagements with both the royal family and Theresa May.
When the royal party and their guests stepped from the palace the American national anthem was played and Mr Trump was invited to inspect an Army guard of honour.
Prince Charles accompanied the President as he strode onto the lawns to inspect the waiting troops formed up in two lines with the guardsmen wearing their famous scarlet tunics and bearskins.
Among the soldiers, who when not performing ceremonial duties are fighting servicemen, was Guardsman Joshua Young-Hastings from Wandsworth, south London.
He was the tallest soldier in the guard of honour and played American Football for the London Warriors before joining the Army.
The guardsman was scouted for a professional career with America's National Football League and was awarded a half scholarship with a Texas university but chose the Grenadier Guards over a sporting career.
Mr Trump took his time as he inspected the Guard of Honour, formed by Nijmegen Company Grenadier Guards.
He walked ahead of Prince Charles and strolled alongside Captain of the Guard Hamish Hardy.
The President stopped to chat to a number of the soldiers at length.
Dr Trevor McCrisken, Professor of politics at the University of Warwick, says Mr Trump has come to London with an agenda.
"He particularly wants to talk about the intelligence issues around the 5G network in the UK," Dr McCrisken said.
"I know, from what I've been hearing that Theresa May has various foreign policy issues on her list to talk to him about as well, including China but also Iran and also climate change."
Dr McCrisken further added that "Trump has not been the greatest supporter of the NATO alliance" and he thinks Theresa May will be "asserting the importance of that alliance".
With D-Day commemoration taking place this week, he says it's an "important reminder of how important that that transatlantic security relationship is".
Elsewhere, royal gun salutes were fired in Green Park and at the Tower of London to mark the Trumps' arrival.
President Trump and the First Lady, Melania Trump then visited Westminster Abbey where the President laid a wreath at the Grave of the Unknown Warrior.
On Monday evening, the Trumps, headed to Buckingham Palace for a state banquet with the Queen, the Prince of Wales and the Duchess of Cornwall.
During the banquet, the Queen expressed strong support for the international institutions set up after the Second World War to preserve peace.
Mr Trump has repeatedly criticised bodies such as the United Nations and NATO.
Her Majesty also said the alliance between Britain and America has helped to ensure the "safety and prosperity" of both countries for decades.
The trip has been surrounded by some controversy.
Over the weekend the President called on Britain to be ready to leave the European Union without a deal and refuse to pay the £39 billion divorce bill if Brussels refuses to meet its demands.
He also urged the Government to send Nigel Farage into the negotiations.
He has also been on Twitter to deny calling the Duchess of Sussex "nasty" after he was confronted with comments she made before the 2016 US elections saying she would leave the country if he won.
Protests in the UK, including rallies in London, Manchester, Belfast, Birmingham and Nottingham are planned.
Both the Stop Trump Coalition and Stand Up to Trump protest groups said they would be present.
The "Trump baby" blimp, made for his visit last year, is also expected to make an appearance.