HEIDELBERG, GERMANY - JULY 20:  Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge arrive for a visit of the German Cancer Research Center on the second day of their visit to Germany on July 20, 2017 in Heidelberg, Germany. The Duke and Duchess of Cambridge will meet researchers including Nobel Prize winner prof. Dr. Harald zur Hausen, and visit the stem cell research lab. The royal couple are on a three-day trip to Germany that includes visits to Berlin, Hamburg and Heidelberg.  (Photo by Thomas Niedermueller/Getty Images)