Four men have been arrested after photos of Donald Trump and Jeffrey Epstein were projected onto Windsor Castle on Tuesday as the U.S. president arrived in the U.K. for his second state visit.

The Thames Valley Police service said in a statement that four adults were arrested on suspicion of malicious communications following an “unauthorized projection” at Windsor Castle, which they described as a “public stunt.” The group was still in custody as of Wednesday morning.

King Charles, Prince William and his wife Catherine greeted Trump at their royal residence on Wednesday, hours after the images of the president — as well as of a birthday letter he allegedly wrote to the convicted sex offender more than 20 years ago, the authenticity of which the White House has denied — were broadcast across the building.

A van could also be seen outside the castle, around 25 miles from London, that showed a photo of Epstein and Trump and displayed the message: “Welcome to the U.K., Donald.”

While in the U.K., the president and first lady Melania are set to have lunch with the royal family as well as visit Queen Elizabeth II’s tomb and attend a traditional state banquet in Windsor.

The visit comes a week after British prime minister Keir Starmer fired Peter Mandelson, the U.K.’s ambassador to the U.S., over his relationship with Epstein, who died by suicide in 2019.

Trump has never been officially accused of wrongdoing in connection with the former financier, though protestors have vowed to gather to object to his visit. London’s Metropolitan Police said more than 1,600 officers would be deployed across the city on Wednesday ahead of a demonstration planned by a group called the Stop Trump Coalition.