King Charles III and Queen Camilla are visiting the US - the first British state visit to the country since Queen Elizabeth II's visit in 2007.
The trip, which comes as the US approaches the 250th anniversary of its independence from Britain, is meant to celebrate the strong relationship between the two countries.
State visits are taken when a head of state is invited for a formal stay by another country, in this case the US. As heads of government, British prime ministers conduct "official visits" or "working visits", but not state visits.
The royal couple will visit Washington DC, New York and Virginia between 27 and 30 April. Here's what you need to know.
King Charles and Queen Camilla's first engagement will be a private afternoon tea with their hosts, President Donald Trump and First Lady Melania Trump, on Monday.
Following tea, the president and first lady will give the royal couple a tour of the newly expanded White House Beehive on the South Lawn.
Later that day, there will be a garden party, with guests from the UK and US meeting the royal visitors at the British ambassador's residence.
Garden parties are part of royal tradition, but it has been decades since the British Royal Family hosted such an event while in America. King George VI and Queen Elizabeth hosted a garden party at the embassy in Washington in 1939.
The Trumps will see the royals again on Tuesday for a formal welcome at the White House, which will feature a ceremonial military review.
The ceremony, part of a tradition that dates back to the 18th century, will feature the US Marine Band playing the national anthems of both countries. The Presidential Salute Battery will also conduct a 21-gun cannon salute.
Trump will also deliver remarks on the South Lawn, where thousands of guests will gather, including cabinet officials, members of Congress , the UK's official delegation, military families and students from the British International School of Washington.
The Trumps will then exchange gifts with the King and Queen and participate in a receiving line for delegations from both countries before the King and Trump hold a bilateral meeting.
Meanwhile, the Queen and first lady will attend a cross-cultural educational event with American students where virtual reality headsets and AI-enabled glasses will teach participants about the histories of both the US and the UK.
In the evening, the Trumps will host an official state dinner for the royal couple in the East Room of the White House.
Also on Tuesday, the King will give a speech to both houses of the US Congress.
The event will be the second time a British monarch has addressed Congress, after Queen Elizabeth II gave a speech during her 1991 state visit.
Trump and the King will make further speeches at the state dinner on Tuesday evening.
Concerns arose over the trip's security after a suspected gunman tried to storm the White House Correspondents' Dinner in Washington on Saturday night. Chief Secretary to the UK prime minister Darren Jones told BBC's Sunday with Laura Kuenssberg that "further discussions [on security] will be taking place today", and "there will be appropriate security in place in relation to the risk".
Buckingham Palace announced on Sunday evening the visit would continue as planned.
"The King and Queen are most grateful to all those who have worked at pace to ensure this remains the case and are looking forward to the Visit getting underway tomorrow," the Palace said in a statement.
When asked in a phone interview with the BBC whether the visit could help repair the relationship between the US and the UK, Trump said: "Absolutely. He's fantastic. He's a fantastic man. Absolutely the answer is 'yes'."
The president added: "I know him well, I've known him for years. He's a brave man, and he's a great man. They would absolutely be a positive."
Following two days in the US capital, the royal couple will head to New York.
While there, they will visit the 9/11 Memorial and meet first responders and families of victims of the 2001 attacks on Wednesday.
New York City Mayor Zohran Mamdani is also expected to attend the event, but he will not meet privately with the King, his office said.
The King will then visit a community organisation and a gathering of business leaders, while the Queen will go to a literary event marking the 100th birthday of the children's character Winnie the Pooh.
In the evening, the pair will head to a glitzy reception focused on the creative industries. There could be some high-profile celebrities in attendance, though specific names have not been released.
After the King and Queen conclude their time in New York, they return to Washington, where the Trumps will say a formal goodbye to the pair on Thursday.
A wreath will be laid in honour of fallen soldiers from both nations, marking the US and UK military alliance.
The King and Queen are then set to travel to Virginia to visit a national park and learn about the region's Appalachian culture, including meeting indigenous Americans. They will also join a community party celebrating the 250th anniversary of American independence.
After leaving the US, the King will pay a visit to Bermuda, where he is also head of state. It will be his first royal visit as monarch to a British overseas territory, before returning to the UK.
The royal couple will not be meeting the King's son, the Duke of Sussex, and his wife, Meghan, the BBC understands.
The couple, who are no longer working royals, live in California and sources suggest neither Prince Harry nor Meghan will meet the monarch.
There have also been calls for the King and Queen to meet survivors of the late sex offender Jeffrey Epstein during their visit.
The King's brother, Andrew Mountbatten-Windsor, who had links to Epstein, was arrested in the UK on suspicion of misconduct in public office in February. The King's brother has consistently and strenuously denied any wrongdoing.
US Congressman Ro Khanna has called for King Charles to meet survivors of Epstein. The brother and sister-in-law of the late Virginia Giuffre also echoed the call in an interview with the BBC's Newsnight programme.
The BBC understands, however, that the King will not hold a meeting because of concerns about potentially jeopardising the ongoing legal processes and police investigations.
It is expected the Queen will meet representatives of groups campaigning against domestic abuse and violence against women at some events during the four-day visit.
