Giant projections of Donald Trump alongside paedophile Jeffrey Epstein have been beamed on to Windsor Castle by protesters as the US president arrived in the UK for his second state visit.
Mr Trump has faced mounting questions about his relationship with the disgraced billionaire after messages allegedly sent to him by the US president were published earlier this month.
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The apparent notes - which Mr Trump denies having written - appeared in a 2003 "birthday book" for Epstein.
Four people were arrested on Tuesday on suspicion of malicious communications after the images of Mr Trump and Epstein appeared on the castle, Thames Valley Police said.
The force said they were a 60-year-old man from East Sussex, a 36-year-old man from London, a 37-year-old man from Kent and a 50-year-old man from London.
"Our officers responded swiftly to stop the projection and four people have been arrested," said Chief Superintendent Felicity Parker.
"We are conducting a thorough investigation with our partners into the circumstances surrounding this incident and will provide further updates when we are in a position to do so."
Two men were also arrested for breaching airspace restrictions in place for Mr Trump's visit.
The president is being feted with a stay in Windsor Castle, where he will be hosted by the King and treated to a ceremonial welcome on Wednesday and later, a lavish state banquet.
The Prince and Princess of Wales will meet the president and first lady Melania Trump in the grounds of the Windsor estate, where he will spend the day, before heading to the prime minister's country residence Chequers on Thursday.
It is hoped the Queen - who pulled out of attending the Duchess of Kent's funeral on Tuesday after suffering from acute sinusitis - will recover in time to attend the busy run of royal events.
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There are no public-facing engagements for the president throughout his 48-hour state visit.
Thousands of people expected to take part in a major protest against his stay in central London today.
The Metropolitan Police said it is preparing for "a significant operation" with as many as 50 protest groups expected to take part.
More than 1,600 officers will be deployed, including 500 assisting from other forces.
A small group of protesters from the Stop Trump Coalition were in Windsor on Tuesday night.
Two protesters from the activist group Fossil Free London were escorted out of a dinner organised by Republicans Overseas UK at Windsor Guildhall in the Berkshire town.
They chanted "how many will you kill if you drill baby drill" and unfurled a banner that said: "Oily Money Kills" at the event.
Speaking to reporters mid-flight, Mr 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".
(c) Sky News 2025: Arrests after Trump-Epstein images projected on to Windsor Castle