U.S. President Barack Obama plays table tennis against students with British Prime Minister David Cameron at the Globe Academy in London May 24, 2011.

U.S. President Barack Obama and British Prime Minister David Cameron each eat hot dogs at a first round "First Four" game of the NCAA Division I Men's Basketball Tournament between Mississippi Valley State and Western Kentucky at the University of Dayton Arena in Ohio, March 13, 2012.

British Prime Minister Tony Blair and his wife Cherie sit down to dinner with President Bill Clinton and his wife Hillary, May 29, 1997. REUTERS/Stringer

British Prime Minister Theresa May looks over toward U.S. President Barack Obama during the luncheon at the United Nations General Assembly in New York September 20, 2016.

U.S. President Donald Trump and British Prime Minister Theresa meet at Chequers in Buckinghamshire, Britain July 13, 2018.

President Bill Clinton toasts with British Prime Minister John Major during a formal dinner at the Prime Minister's official residence at No. 10 Downing Street, November 29, 1995. REUTERS/Stringer

President Reagan drives Britain Prime Minister Margaret Thatcher toward their meeting in Camp David on November 15, 1986, after her arrival by helicopter from Washington. REUTERS/Anthony Hayward - GF1DURFJZKAF

President Bill Clinton holds a cowboy hat as he hugs British Prime Minister Tony Blair upon his arrival at The Fort Restaurant June 21, 1997 at the Denver Summit of the Eight. REUTERS/Gary Hershorn

U.S. President Donald Trump meets with British Prime Theresa Minister May in the White House Oval Office in Washington, U.S., January 27, 2017.

British Prime Minister Gordon Brown smiles during a joint news conference with U.S. President Barack Obama (R) at the Foreign and Commonwealth Office in London April 1, 2009. World leaders will have their work cut out at a G20 summit where Obama makes his first major international sortie, under perhaps more pressure than anyone to show that the country where the crisis began can lead the way out.

British Prime Minister Margaret Thatcher and President Reagan share a laugh during a meeting of the Allied leaders in New York on October 24, 1985.

U.S. President Barack Obama (L) welcomes Britain's Prime Minister David Cameron aboard Air Force One as they depart to go to Ohio to watch one of the opening games of the NCAA Men's Basketball tournament, from Andrews Air Force Base, Maryland, March 13, 2012.

U.S. President George W. Bush and British Prime Minister Tony Blair leave the East Room of the White House after speaking to reporters about Iraq in Washington May 25, 2006. British Prime Minister Tony Blair said on Thursday it was the duty of the entire international community, as well as Britain and the United States, to support the new Iraqi government.

British Prime Minister Margaret Thatcher and U.S. Vice President George Bush pause for the press on the porch of the Vice President's residence before a breakfast meeting November 15, 1986. The Prime Minister will travel to Camp David following the breakfast for a meeting with President Reagan.

U.S. President George W. Bush shakes hands with British Prime Minister Tony Blair moments after receiving a note from U.S. Secretary of Defense Donald Rumsfeld given to him by National Security Advisor Condoleezza Rice informing the president "Iraq is sovereign" during the opening working session of the NATO Summit at the Istanbul Convention and Exhibition Center in Istanbul, Turkey, June 28, 2004. The president returned the note to Dr. Rice after writing, "Let freedom reign."

U.S President George W. Bush (R) puts his hand on the back of Britain's Prime Minister Tony Blair (L) as they enter 10 Downing Street in London, November 20, 2003. Deadly blasts in Istanbul overshadowed President Bush's state visit to Britain on Thursday as he prepared to meet Prime Minister Tony Blair for talks on Iraq.

U.S. President Donald Trump greets British Prime Minister Theresa May as she arrives at the White House in Washington, U.S., January 27, 2017.

Britain's Prime Minister Theresa May poses for a photograph with U.S. President Donald Trump at Chequers near Aylesbury, Britain July 13, 2018.

Britain's Prime Minister Theresa May and U.S. President Donald Trump walk to a joint news conference at Chequers, the official country residence of the Prime Minister, near Aylesbury, Britain, July 13, 2018.

U.S. President Barack Obama and Britain's Prime Minister Gordon Brown walk through the Colonnade at the White House in Washington, March 3, 2009. Brown will press Obama for details on his plans to fix the ailing U.S. financial sector in talks on Tuesday that will focus on the global economic crisis. REUTERS/Jim Young

President Bill Clinton and Hillary sing the U.S. national anthem, standing alongside British Prime Minister John Major and wife Norma during a D-Day commemoration ceremony at the American Cemetery and Memorial in Cambridge June 4, 1994. REUTERS/Stringer

Britain's Prime Minister Gordon Brown (R) and U.S. President Barack Obama leave 10 Downing Street in London April 1, 2009. World leaders will have their work cut out at a G20 summit where Obama makes his first major international sortie, under perhaps more pressure than anyone to show that the country where the crisis began can lead the way out.

President Bill Clinton and British Prime Minister Tony Blair speak together during the NATO signing ceremony at the Eysee Palace May 27, 1997. REUTERS/Charles Platiau

U.S. President Barack Obama and Britain's Prime Minister Gordon Brown walk through the Colonnade at the White House in Washington, March 3, 2009. Brown will press Obama for details on his plans to fix the ailing U.S. financial sector in talks on Tuesday that will focus on the global economic crisis.

President Reagan drives Britain Prime Minister Margaret Thatcher toward their meeting in Camp David on November 15, 1986, after her arrival by helicopter from Washington. Imaged used for illustrative purpose