President Barack Obama is to travel to Britain next month, the White House has confirmed.
The US leader will have a private lunch with the Queen at Windsor Castle and stage a joint conference with David Cameron at 10 Downing Street.
It is likely to be the president's last visit to the UK before his term in office ends in January and comes after he made clear his desire for Britain to remain in the European Union (EU).
He said the UK's EU membership gave America "much greater confidence about the strength of the transatlantic union" ahead of the June 23 referendum.
But the US president's intervention was described as a "piece of outrageous and exorbitant hypocrisy" by Boris Johnson, who is campaigning for Britain to leave the EU.
Mr Obama is also expected to arrive in the UK just after the Queen celebrates her 90th birthday on April 21.
A White House spokesman said: "The visit will allow the president to offer his gratitude to the British government and people for their stalwart partnership with his administration and the American people throughout his presidency."
Mr Obama and his family have developed a close affinity with the British monarchy during his term in office.
When the Queen hosted the US leader and his wife, Michelle, at Buckingham Palace during a state visit in 2011, the First Lady was seen putting her arm around the monarch's waist, showing how the women had become firm friends.
Mr Obama will visit Saudi Arabia on April 21 for a summit of the Gulf Cooperation Council, including leaders of Bahrain, Kuwait, Oman, Qatar, Saudi Arabia, and the United Arab Emirates. They will discuss the fight against the Islamic State terror group and other regional security concerns.
Following his UK visit, the US president will travel to Germany to meet Chancellor Angela Merkel and visit Hannover Messe, the world's largest trade show for industrial technology.