HEIDELBERG, GERMANY - JULY 20:  Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge, accompanied by Baden-Wurttemberg's Minister President Winfried Kretschmann (Alliance '90/Greens) and his wife Gerlinde, listen to Dr. Michael Milsom, Group Leader for Experimental Hematology during a visit to the German Cancer Research Institute on day 2 of their official visit to Germany on July 20, 2017 in Heidelberg, Germany. (Photo by Dominic Lipinski - Pool/Getty Images)