Britain's Prince William, Duke of Cambridge and New Zealand film maker Peter Jackson attend the world premiere of Peter Jackson's film "They Shall Not Grow Old" during the BFI London Film Festival in London, Britain October 16, 2018. Daniel Leal-Olivas/Pool via REUTERS

Britain's Prince William, Duke of Cambridge speaks with Diane Lees, director-general of Imperial War Museums and commissioners and producers of "14-18 Now" as he attends the world premiere of Peter Jackson's film "They Shall Not Grow Old" during the BFI London Film Festival in London, Britain October 16, 2018. Daniel Leal-Olivas/Pool via REUTERS

Britain's Prince William, Duke of Cambridge shakes hands with New Zealand film maker Peter Jackson as he attends the world premiere of Peter Jackson's film "They Shall Not Grow Old" during the BFI London Film Festival in London, Britain October 16, 2018. Daniel Leal-Olivas/Pool via REUTERS

Britain's Prince William, Duke of Cambridge and New Zealand film maker Peter Jackson attend the world premiere of Peter Jackson's film "They Shall Not Grow Old" during the BFI London Film Festival in London, Britain October 16, 2018. Daniel Leal-Olivas/Pool via REUTERS

Britain's Prince William, Duke of Cambridge speaks with Diane Lees, director-general of Imperial War Museums and commissioners and producers of "14-18 Now" as he attends the world premiere of Peter Jackson's film "They Shall Not Grow Old" during the BFI London Film Festival in London, Britain October 16, 2018. Daniel Leal-Olivas/Pool via REUTERS

Britain's Prince William, Duke of Cambridge shakes hands with New Zealand film maker Peter Jackson as he attends the world premiere of Peter Jackson's film "They Shall Not Grow Old" during the BFI London Film Festival in London, Britain October 16, 2018. Daniel Leal-Olivas/Pool via REUTERS

Britain's Prince William, Duke of Cambridge attends the world premiere of Peter Jackson's film "They Shall Not Grow Old" during the BFI London Film Festival in London, Britain October 16, 2018. Daniel Leal-Olivas/Pool via REUTERS

Britain's Prince William, Duke of Cambridge speaks with New Zealand film maker Peter Jackson as he attends the world premiere of Peter Jackson's film "They Shall Not Grow Old" during the BFI London Film Festival in London, Britain October 16, 2018. Daniel Leal-Olivas/Pool via REUTERS

Britain's Prince William, Duke of Cambridge (L) and New Zealand film maker Peter Jackson (R) attend the world premiere of Peter Jackson's film "They Shall Not Grow Old" during the BFI London Film Festival in London, Britain October 16, 2018. Daniel Leal-Olivas/Pool via REUTERS

Britain's Prince William, Duke of Cambridge speaks with New Zealand film maker Peter Jackson as he attends the world premiere of Peter Jackson's film "They Shall Not Grow Old" during the BFI London Film Festival in London, Britain October 16, 2018. Daniel Leal-Olivas/Pool via REUTERS

Britain's Prince William, Duke of Cambridge and New Zealand film maker Peter Jackson attend the world premiere of Peter Jackson's film "They Shall Not Grow Old" during the BFI London Film Festival in London, Britain October 16, 2018. Daniel Leal-Olivas/Pool via REUTERS

Britain's Prince William, Duke of Cambridge attends the world premiere of Peter Jackson's film "They Shall Not Grow Old" during the BFI London Film Festival in London, Britain October 16, 2018. Daniel Leal-Olivas/Pool via REUTERS

Britain's Prince William, Duke of Cambridge shakes hands with New Zealand film maker Peter Jackson as he attends the world premiere of Peter Jackson's film "They Shall Not Grow Old" during the BFI London Film Festival in London, Britain October 16, 2018. Daniel Leal-Olivas/Pool via REUTERS

Britain's Queen Elizabeth waves next to Prince Charles and PrinceÊWilliam, Duke of Cambridge, during a special concert "The Queen's Birthday Party" to celebrate her 92nd birthday at the Royal Albert Hall in London, Britain April 21, 2018. Andrew Parsons/Pool via Reuters

Britain'sÊQueenÊElizabeth waves next to Prince Charles and PrinceÊWilliam, Duke of Cambridge, during a special concert "The Queen's Birthday Party" to celebrate her 92nd birthday at the Royal Albert Hall in London, Britain April 21, 2018. Andrew Parsons/PoolÊviaÊReuters

A boy rushes to greet Britain's Prince William (L), the Duke of Cambridge, during a visit to a Premier League training camp at Nanyang Secondary School in Shanghai, March 3, 2015. REUTERS/Carlos Barria (CHINA - Tags: ROYALS)

Britain's Prince William (rear L) poses for a group picture with students during a visit to a Premier League training camp at Nanyang Secondary School in Shanghai March 3, 2015. REUTERS/Carlos Barria (CHINA - Tags: ROYALS SPORT SOCCER)

Britain's Prince William, the Duke of Cambridge, attends the opening of the "Great Festival of Creativity," at the Long Museum in Shanghai, March 2, 2015. REUTERS/Carlos Barria (CHINA - Tags: POLITICS ROYALS)

Britain's Prince William, the Duke of Cambridge, attends the opening of the "Great Festival of Creativity," at the Long Museum in Shanghai, March 2, 2015. REUTERS/Carlos Barria (CHINA - Tags: POLITICS ROYALS)

Britain's Prince William, the Duke of Cambridge, attends the opening of the "Great Festival of Creativity," at the Long Museum in Shanghai, March 2, 2015. REUTERS/Aly Song (CHINA - Tags: POLITICS ROYALS)

Britain's Prince William, the Duke of Cambridge, attends the opening of the "Great Festival of Creativity," at the Long Museum in Shanghai, March 2, 2015. REUTERS/Aly Song (CHINA - Tags: POLITICS ROYALS)

Britain's Prince William (stage C), the Duke of Cambridge, attends the opening of the "Great Festival of Creativity," at the Long Museum in Shanghai, March 2, 2015. REUTERS/Carlos Barria (CHINA - Tags: POLITICS ROYALS)

Britain's Prince William (front 2nd R), the Duke of Cambridge, arrives for the opening of the "Great Festival of Creativity," at the Long Museum in Shanghai, March 2, 2015. REUTERS/Carlos Barria (CHINA - Tags: POLITICS ROYALS)

Britain's Prince William (C), the Duke of Cambridge, attends the opening of the "Great Festival of Creativity," at the Long Museum in Shanghai, March 2, 2015. REUTERS/Carlos Barria (CHINA - Tags: POLITICS ROYALS)

Britain's Prince William (C), the Duke of Cambridge, attends the opening of the "Great Festival of Creativity," at the Long Museum in Shanghai, March 2, 2015. REUTERS/Carlos Barria (CHINA - Tags: POLITICS ROYALS)

Britain's Prince William (C) chats with Chinese officials as he tours the Forbidden City during his visit to Beijing, March 2, 2015. REUTERS/Andy Wong/Pool (CHINA - Tags: POLITICS ROYALS)

Britain's Prince William (C) is guided by Chinese officials as he tours the Forbidden City during his visit to Beijing March 2, 2015. REUTERS/Andy Wong/Pool (CHINA - Tags: ROYALS POLITICS)

Britain's Prince William (2nd R) is guided by Chinese officials as he tours the Forbidden City during his visit to Beijing March 2, 2015. REUTERS/Andy Wong/Pool (CHINA - Tags: ROYALS POLITICS)

Britain's Prince William (2nd R) is guided by Chinese officials as he tours the Forbidden City during his visit to Beijing March 2, 2015. REUTERS/Andy Wong/Pool (CHINA - Tags: ROYALS POLITICS)

Britain's Prince William meets Chinese President Xi Jinping (not pictured) at the Great Hall of the People in Beijing, March 2, 2015. REUTERS/Feng Li/Pool (CHINA - Tags: ROYALS POLITICS)

Britain's Prince William meets Chinese President Xi Jinping (not pictured) at the Great Hall of the People in Beijing, March 2, 2015. REUTERS/Feng Li/Pool (CHINA - Tags: ROYALS POLITICS)

Britain's Prince William, Duke of Cambridge speaks with people at the British Ambassador's official residence in Beijing, March 2, 2015. REUTERS/Fred Dufour/Pool (CHINA - Tags: ROYALS POLITICS)

Britain's Prince William (L) gestures next to China's President Xi Jinping during a meeting at the Great Hall of the People in Beijing March 2, 2015. REUTERS/Feng Li/Pool (CHINA - Tags: POLITICS ROYALS)

Britain's Prince William, Duke of Cambridge speaks with a Chinese artist in front of "Shaun the Sheep" sculptures at the British Ambassador's official residence in Beijing, March 2, 2015. REUTERS/Fred Dufour/Pool (CHINA - Tags: POLITICS ROYALS ENTERTAINMENT)

Britain's Prince William, Duke of Cambridge, paints the eye of a "Shaun the Sheep" sculpture at the British Ambassador's official residence in Beijing, March 2, 2015. REUTERS/Fred Dufour/Pool (CHINA - Tags: POLITICS ROYALS ENTERTAINMENT)

Britain's Prince William, Duke of Cambridge, poses after painting the eye of a "Shaun the Sheep" sculpture at the British Ambassador's official residence in Beijing, March 2, 2015. REUTERS/Fred Dufour/Pool (CHINA - Tags: POLITICS ROYALS ENTERTAINMENT)

Britain's Prince William, Duke of Cambridge, poses after painting the eye of a "Shaun the Sheep" sculpture at the British Ambassador's official residence in Beijing, March 2, 2015. REUTERS/Fred Dufour/Pool (CHINA - Tags: POLITICS ROYALS ENTERTAINMENT)

Britain's Prince William, Duke of Cambridge, looks on after painting the eye of a "Shaun the Sheep" sculpture at the British Ambassador's official residence in Beijing, March 2, 2015. REUTERS/Fred Dufour/Pool (CHINA - Tags: POLITICS ROYALS ENTERTAINMENT)

Britain's Prince William (R) leaves the Great Hall of the People after meeting China's President Xi Jinping in Beijing March 2, 2015. REUTERS/Feng Li/Pool (CHINA - Tags: POLITICS ROYALS)

Britain's Prince William (L), Duke of Cambridge, is guided by Matthew Hu, China's representative of the Prince's School of Traditional Arts while he visits the Shijia Hutong in Beijing March 2, 2015.
REUTERS/Kim Kyung-Hoon (CHINA - Tags: SOCIETY ROYALS)

Britain's Prince William, Duke of Cambridge, is guided by staff members of the British Embassy in China while he visits the Shijia Hutong in Beijing March 2, 2015. REUTERS/Kim Kyung-Hoon (CHINA - Tags: SOCIETY ROYALS)

Britain's Prince William, Duke of Cambridge, meets with Chinese children and physically handicapped young people while he visits the Shijia Hutong in Beijing March 2, 2015.
REUTERS/Kim Kyung-Hoon (CHINA - Tags: SOCIETY ROYALS)

Britain's Prince William, Duke of Cambridge, is seen through a window bearing the reflection of a red lantern during his visit to the Shijia Hutong in Beijing March 2, 2015.
REUTERS/Kim Kyung-Hoon (CHINA - Tags: SOCIETY ROYALS)

Britain's Prince William (R), Duke of Cambridge, is guided by Matthew Hu, China's representative of the Prince's School of Traditional Arts while he visits the Shijia Hutong in Beijing March 2, 2015. REUTERS/Kim Kyung-Hoon (CHINA - Tags: SOCIETY ROYALS)

Britain's Prince William (front R) arrives at the Great Hall of the People before his meeting with China's President Xi Jinping in Beijing March 2, 2015. REUTERS/Feng Li/Pool (CHINA - Tags: POLITICS ROYALS)

Britain's Prince William, Duke of Cambridge, paints the eye of a "Shaun the Sheep" sculpture at the British Ambassador's official residence in Beijing, March 2, 2015. REUTERS/Fred Dufour/Pool (CHINA - Tags: POLITICS ROYALS ENTERTAINMENT)

Britain's Prince William, Duke of Cambridge, paints the eye of a "Shaun the Sheep" sculpture at the British Ambassador's official residence in Beijing, March 2, 2015. REUTERS/Fred Dufour/Pool (CHINA - Tags: POLITICS ROYALS ENTERTAINMENT)

Britain's Prince William (L) meets China's President Xi Jinping at the Great Hall of the People in Beijing March 2, 2015. REUTERS/Feng Li/Pool (CHINA - Tags: POLITICS ROYALS)

Britain's Prince William meets China's President Xi Jinping at the Great Hall of the People in Beijing March 2, 2015. REUTERS/Feng Li/Pool (CHINA - Tags: POLITICS ROYALS)

Britain's Prince William (L) meets China's President Xi Jinping at the Great Hall of the People in Beijing March 2, 2015. REUTERS/Feng Li/Pool (CHINA - Tags: POLITICS ROYALS)

Britain's Prince William (L) meets China's President Xi Jinping at the Great Hall of the People in Beijing March 2, 2015. REUTERS/Feng Li/Pool (CHINA - Tags: POLITICS ROYALS)

Britain's Prince William meets China's President Xi Jinping at the Great Hall of the People in Beijing March 2, 2015. REUTERS/Feng Li/Pool (CHINA - Tags: POLITICS ROYALS)

Britain's Prince William (R) arrives in Eden Park with New Zealand's Prime Minister John Key while in New Zealand for a 3-day visit, in Auckland January 17, 2010. REUTERS/Nigel Marple/Pool (NEWZEALAND - Tags: ROYALS POLITICS)

Britain's Prince William (R) arrives in Eden Park with New Zealand's Prime Minister John Key while in New Zealand for a 3-day visit, in Auckland January 17, 2010. REUTERS/Nigel Marple/Pool (NEWZEALAND - Tags: ROYALS POLITICS)

Britain's Prince William concentrates at the helm onboard America's Cup yacht "NZL40" on the Waitemata Harbour while in New Zealand for a 3-day visit, in Auckland January 17, 2010. REUTERS/Nigel Marple (NEWZEALAND - Tags: ROYALS POLITICS)

Britain's Prince William gestures while onboard America's Cup yacht "NZL40" on the Waitemata Harbour while in New Zealand for a 3-day visit, in Auckland January 17, 2010. REUTERS/Nigel Marple (NEWZEALAND - Tags: ROYALS POLITICS)

Britain's Prince William laughs while at the helm of America's Cup yacht "NZL40" on the Waitemata Harbour while in New Zealand for a 3 day visit, in Auckland January 17, 2010. REUTERS/Nigel Marple (NEWZEALAND - Tags: ROYALS POLITICS)

Britain's Prince William gestures next to a crew member onboard America's Cup yacht "NZL40" on the Waitemata Harbour while in New Zealand for a 3 day visit, in Auckland January 17, 2010. REUTERS/Nigel Marple (NEWZEALAND - Tags: ROYALS POLITICS)

Britain's Prince William (2nd R) steers America's Cup yacht "NZL40" on the Waitemata Harbour while in New Zealand for a 3 day visit, in Auckland January 17, 2010. REUTERS/Nigel Marple (NEWZEALAND - Tags: ROYALS POLITICS)

Britain's Prince William waves to supporters onboard America's Cup yacht "NZL40" on the Waitemata Harbour while in New Zealand for a 3 day visit, in Auckland January 17, 2010. REUTERS/Nigel Marple (NEWZEALAND)