GDANSK, POLAND - JULY 18:  Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge meet former prisoners of the Stutthof concentration camp as they visit the former Nazi German concentration camp during an official visit to Poland and Germany on July 18, 2017 near Gdansk, Poland.  (Photo by Bruce Adams-Pool/Getty Images)
GDANSK, POLAND - JULY 18:  Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge join a street party on July 18, 2017 in Gdansk, Poland.  (Photo by Arthur Edwards / Pool / Getty Images)
GDANSK, POLAND - JULY 18:  General view of the Gdansk Shakespeare Theatre during an official visit from the Duke and Duchess of Cambridge to Poland and Germany on July 18, 2017 in Gdansk, Poland.  (Photo by Chris Jackson - Pool/Getty Images)
GDANSK, POLAND - JULY 18: Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge walk through the shipyard gates during a visit to the European Solidarity Movement museum, the birthplace of Poland's Solidarity movement that helped topple Communist rule on July 18, 2017 in Gdansk, Poland.  (Photo by Dominic Lipinski / Pool / Getty Images)
GDANSK, POLAND - JULY 18:  Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge lay flowers at the Solidarity Monument at the European Solidarity Centre during an official visit to Poland and Germany on July 18, 2017 in Gdansk, Poland.  (Photo by Samir Hussein/WireImage)