U.S. President Barack Obama and first lady Michelle Obama depart Winfield House in London to have lunch with Queen Elizabeth II at Windsor Castle April 22, 2016. REUTERS/Kevin Lamarque
U.S. President Barack Obama and first lady Michelle Obama are greeted by Queen Elizabeth II and Prince Philip, Duke of Edinburgh upon their arrival for lunch at Windsor Castle in Windsor, Britain April 22, 2016. REUTERS/Kevin Lamarque
Britain's Queen Elizabeth II and the Duke of Edinburgh stand with the President and First Lady of the United States Barack Obama and his wife Michelle (both centre), in the Oak Room at Windsor Castle ahead of a private lunch hosted by the Queen in Windsor, Britain, April 22, 2016. REUTERS/John Stillwell
The arrival of the President of the United States and First Lady with HRH the Queen driven by the Prince Philip, Duke of Edinburgh, at the Sovereign's Entrance in the Quadrangle of Windsor Castle, Britain April 22, 2016. REUTERS/Geoff Pugh
Britain's Prince William, his wife Catherine, Duchess of Cambridge, and Prince Harry, wait for U.S. President Barack Obama and first lady Michelle Obama to arrive for dinner at Kensington Palace in London, Britain April 22, 2016. REUTERS/Chris Jackson
U.S. President Barack Obama and first lady Michelle Obama react upon arrival at Kensington Palace before a dinner with Britain's Prince William and his wife Catherine, Duchess of Cambridge, and Prince Harry, in London, Britain April 22, 2016. REUTERS/Chris Jackson
U.S. President Barack Obama holds an umbrella as he and first lady Michelle Obama are greeted by Britain's Prince William, his wife Catherine, Duchess of Cambridge, and Prince Harry, upon arrival for dinner at Kensington Palace in London, Britain April 22, 2016. REUTERS/Kevin Lamarque
Britain's Prince Harry greets U.S. first lady Michelle Obama while President Barack Obama, Britain's Prince William and his wife Catherine, Duchess of Cambridge, and Prince Harry, look on before a dinner at Kensington Palace in London, Britain April 22, 2016. REUTERS/Chris Radburn
U.S. President Barrack Obama and First Lady Michelle Obama arrive for dinner at Kensington Palace with Britain's Prince William, his wife Kate and Prince Harry in London, Britain, April 22, 2016. REUTERS/Kevin Lamarque
U.S. President Barack Obama and first lady Michelle Obama visit Kensington Palace for dinner with Britain's Prince William, his wife Catherine, Duchess of Cambridge, and Prince Harry in London, Britain April 22, 2016. REUTERS/Stephen Crowley
Britain's Prince William, Duke of Cambridge speaks with U.S. President Barack Obama before a dinner at Kensington Palace in London, Britain, April 22, 2016. REUTERS/Dominic Lipinski
Britain's Catherine, Duchess of Cambridge speaks with U.S. first lady Michelle Obama before a dinner at Kensington Palace in London, Britain, April 22, 2016. REUTERS/Dominic Lipinski
Handout photo issued by Kensington Palace of Prince George (right) meeting the President of the United States Barack Obama (centre) and First Lady Michelle Obama (behind) at Kensington Palace, London, with Britain's Prince William Friday April 22, 2016. Kensington Palace/Pete Souza/White House Photographer/PA Wire/Handout via Reuters
Handout photo issued by Kensington Palace of US President Barack Obama (2nd right) and Britain's Prince William (right) while Catherine, Duchess of Cambridge plays with Prince George as he rides a rocking horse Friday April 22, 2016. Kensington Palace/PA Wire/Handout via Reuters
Handout photo issued by Kensington Palace of US President Barack Obama (right) talking with Britain's Prince William (2nd right) while Catherine, Duchess of Cambridge plays with Prince George as he rides a rocking horse while the First Lady Michelle Obama talks to Prince Harry (left) Friday April 22, 2016. Kensington Palace/Pete Souza/White House Photographer/PA Wire/Handout via Reuters