Britain's Prince Charles (3rd-R) and  his wife Camilla (C), Duchess of Cornwall, pose in front of the Martin Luther King Memorial on March 18, 2015 in Washington, DC. PrinThe royal couple are on a four-day visit to the US that includes a meeting with US President Barack Obama and a stop in Kentucky.  AFP PHOTO/MANDEL NGAN        (Photo credit should read MANDEL NGAN/AFP/Getty Images)