WASHINGTON, DC - MARCH 19: United States President Barack Obama, right center, hosts Their Royal Highnesses Prince Charles, Prince of Wales, left center, and Camilla, Duchess of Cornwall, left, with Vice President Joe Biden, right, for a meeting in the Oval Office of the White House on March 19, 2015 in Washington, D.C. (Photo by Ron Sachs-Pool/Getty Images)

WASHINGTON, DC - MARCH 19:  United States President Barack Obama, right center, hosts Their Royal Highnesses Prince Charles, Prince of Wales, left center, and Camilla, Duchess of Cornwall, left, with Vice President Joe Biden, right, for a meeting in the Oval Office of the White House on March 19, 2015 in Washington, D.C.  (Photo by Ron Sachs-Pool/Getty Images)