Donald Trump has arrived in the UK for his second state visit, telling reporters Britain is"a very special place".
But as he headed to the residence of the US ambassador to the UK in central London to spend Tuesday night, giant projections of the president alongside paedophile Jeffrey Epstein were beamed on to Windsor Castle by protesters.
It is there he will meet with King Charles later today.
Four people were arrested on "suspicion of malicious communications" after the images of Mr Trump and Epstein appeared on the landmark, Thames Valley Police said.
Mr Trump has faced mounting questions about his relationship with the disgraced late billionaire after messages allegedly sent to him by the president were published by Congress earlier this month .
The apparent notes - which Mr Trump denies having written - appeared in a 2003"birthday book" for Epstein which also included messages from Peter Mandelson, who has since been sacked as Sir Keir Starmer's ambassador to the US over his ties to the financier .
Foreign Secretary Yvette Cooper was among those who greeted the president and First Lady Melania as they disembarked their official plane at Stansted airport on Tuesday evening.
An honour guard of RAF personnel from The King's Colour Squadron lined up as he stepped off the plane.
Trump excited to see 'my friend' Charles
Speaking to reporters mid-flight, Trump said:"My relationship is very good with the UK, and Charles, as you know, who's now King, is my friend.
"It's the first time this has ever happened where somebody was honoured twice. So, it's a great honour."
He told the journalists "everybody is looking forward to it. You're going to have the best pictures".
To mark the president's arrival, a new UK-US tech deal was announced that could generate billions of pounds of investment for Britain.
Sir Keir - who will host Mr Trump at his Chequers country retreat tomorrow - said the deal would deliver"growth, security and opportunity up and down the country".
What will happen today?
The Prince and Princess of Wales will greet the president and his wife in the grounds of the Windsor estate in the morning, before accompanying them to meet the King and Queen for an open-air greeting.
Mr and Mrs Trump, the King, Camilla, William, and Kate will then take part in a carriage procession through the estate to the castle, with the carriage ride joined by the Household Cavalry Mounted Regiment, which will provide a Sovereign's Escort, as well as members of the armed forces and three military bands.
A ceremonial welcome with a guard of honour will be staged in the quadrangle of the castle, as is customary, followed by lunch with the royal family and a visit to see a Royal Collection exhibition within the castle.
The president and his wife will then visit St George's Chapel privately on Wednesday afternoon to lay a wreath on the tomb of Queen Elizabeth II, whom they both met on their first state visit.
They will then be treated to a flypast by the Red Arrows alongside UK and US F-35 military jets on the east lawn at Windsor Castle, as well as a special Beating Retreat military ceremony.
They will then be treated to a flypast by the Red Arrows alongside UK and US F-35 military jets on the east lawn at Windsor Castle, as well as a special Beating Retreat military ceremony.
The traditional grand state banquet is set to follow in the castle's St George's Hall in the evening, with both Mr Trump and the King to give speeches as the event gets underway.
The"tech prosperity deal", announced as Mr Trump touched down, will see the UK and US co-operate in areas including artificial intelligence (AI), quantum computing and nuclear power.
It comes alongside £31bn of investment in Britain from top US tech firms, including £22bn from Microsoft.
'I'm into helping Britain'
It also follows the agreement of an economic deal in May that covered a reduction in some of Mr Trump's tariffs.
However, the government is understood to have given up hope - for now at least - of reducing the president's levy on steel back down to zero. It currently stands at 25%.
Mr Trump had hinted at possible tariff relief for British steel as he boarded Air Force One, telling reporters he was"into helping" Britain on refining the trade deal signed earlier this year.
