Former United Nations Secretary General Ban Ki-moon arrives ahead of the start of the 74th session of the United Nations General Assembly at U.N. headquarters in New York City, New York, U.S., September 24, 2019. REUTERS/Yana Paskova

A man walks past portraits of former United Nations Secretary Generals Kofi Annan (L) and Ban Ki-moon at U.N. headquarters during the 2019 United Nations Climate Action Summit at U.N. headquarters in New York City, New York, U.S., September 23, 2019. REUTERS/Yana Paskova

Former UN Secretary General Ban Ki-moon shakes hand of China's Premier Li Keqiang as he stands near Netherlands' Prime Minister Mark Rutte during the Global Commission on Adaptation ceremony, at the Great Hall of the People in Beijing, China June 27, 2019. Fred Dufour/Pool via REUTERS

Netherlands' Prime Minister Mark Rutte, China's Premier Li Keqiang and Former U.N. Secretary General Ban Ki-moon arrive for the Global Commission on Adaptation ceremony, at the Great Hall of the People in Beijing, China June 27, 2019. Fred Dufour/Pool via REUTERS

Netherlands' Prime Minister Mark Rutte, China's Premier Li Keqiang and Former U.N. Secretary General Ban Ki-moon react next to an official board during the Global Commission on Adaptation ceremony, at the Great Hall of the People in Beijing, China June 27, 2019. Fred Dufour/Pool via REUTERS

Netherlands' Prime Minister Mark Rutte, China's Premier Li Keqiang and Former U.N. Secretary General Ban Ki-moon arrive for the Global Commission on Adaptation ceremony, at the Great Hall of the People in Beijing, China June 27, 2019. Fred Dufour/Pool via REUTERS

Netherlands' Prime Minister Mark Rutte, China's Premier Li Keqiang and Former U.N. Secretary General Ban Ki-moon shake hands next to an official board during the Global Commission on Adaptation ceremony, at the Great Hall of the People in Beijing, China June 27, 2019. Fred Dufour/Pool via REUTERS

China's Premier Li Keqiang speaks to Netherlands' Prime Minister Mark Rutte and Former U.N. Secretary General Ban Ki-moon during the Global Commission on Adaptation ceremony, at the Great Hall of the People in Beijing, China June 27, 2019. Fred Dufour/Pool via REUTERS

Former U.N. Secretary General Ban Ki-moon delivers a speech to China's Premier Li Keqiang and Netherlands' Prime Minister Mark Rutte during the Global Commission on Adaptation ceremony, at the Great Hall of the People in Beijing, China June 27, 2019. Fred Dufour/Pool via REUTERS

Former U.N. Secretary General Ban Ki-moon delivers a speech to China's Premier Li Keqiang and Netherlands' Prime Minister Mark Rutte during the Global Commission on Adaptation ceremony, at the Great Hall of the People in Beijing, China June 27, 2019. Fred Dufour/Pool via REUTERS

Former U.N. Secretary General Ban Ki-moon delivers a speech to China's Premier Li Keqiang and Netherlands' Prime Minister Mark Rutte during the Global Commission on Adaptation ceremony, at the Great Hall of the People in Beijing, China June 27, 2019. Fred Dufour/Pool via REUTERS

Netherlands' Prime Minister Mark Rutte shakes hand with Former U.N. Secretary General Ban Ki-moon during the Global Commission on Adaptation ceremony, at the Great Hall of the People in Beijing, China June 27, 2019. Fred Dufour/Pool via REUTERS

Former U.N. Secretary General Ban Ki-moon delivers a speech to China's Premier Li Keqiang and Netherlands' Prime Minister Mark Rutte during the Global Commission on Adaptation ceremony, at the Great Hall of the People in Beijing, China June 27, 2019. Fred Dufour/Pool via REUTERS

Netherlands' Prime Minister Mark Rutte speaks to China's Premier Li Keqiang and Former U.N. Secretary General Ban Ki-moon during the Global Commission on Adaptation ceremony, at the Great Hall of the People in Beijing, China June 27, 2019. Fred Dufour/Pool via REUTERS

Netherlands' Prime Minister Mark Rutte speaks to China's Premier Li Keqiang and Former U.N. Secretary General Ban Ki-moon during the Global Commission on Adaptation ceremony, at the Great Hall of the People in Beijing, China June 27, 2019. Fred Dufour/Pool via REUTERS

Netherlands' Prime Minister Mark Rutte speaks to China's Premier Li Keqiang and Former U.N. Secretary General Ban Ki-moon during the Global Commission on Adaptation ceremony, at the Great Hall of the People in Beijing, China June 27, 2019. Fred Dufour/Pool via REUTERS

Former U.N. Secretary-General Ban Ki-moon, his wife Yoo Soon-taek, Mukesh Ambani, the Chairman of Reliance Industries, and his wife Nita Ambani pose during a photo opportunity at the wedding ceremony of Mukesh's son Akash Ambani at Bandra-Kurla Complex in Mumbai, India, March 9, 2019. REUTERS/Francis Mascarenhas

Former U.N. secretary-general Ban Ki-moon and his wife Yoo Soon-taek pose during a photo opportunity at the wedding ceremony of Akash Ambani, son of the Chairman of Reliance Industries Mukesh Ambani, at Bandra-Kurla Complex in Mumbai, India, March 9, 2019. REUTERS/Francis Mascarenhas

Chinese President Xi Jinping meets head of the International Olympic Committee's ethics commission, former UN Secretary-General Ban Ki-moon at the Great Hall of the People in Beijing, China, May 15, 2018. REUTERS/Thomas Peter/Pool

Chinese President Xi Jinping meets head of the International Olympic Committee's ethics commission, former UN Secretary-General Ban Ki-moon (not pictured) at the Great Hall of the People in Beijing, China, May 15, 2018. REUTERS/Thomas Peter/Pool

Chinese President Xi Jinping meets head of the International Olympic Committee's ethics commission, former UN Secretary-General Ban Ki-moon (not pictured) at the Great Hall of the People in Beijing, China, May 15, 2018. REUTERS/Thomas Peter/Pool

Chinese President Xi Jinping meets head of the International Olympic Committee's ethics commission, former UN Secretary-General Ban Ki-moon (not pictured) at the Great Hall of the People in Beijing, China, May 15, 2018. REUTERS/Thomas Peter/Pool

Chinese President Xi Jinping meets head of the International Olympic Committee's ethics commission, former UN Secretary-General Ban Ki-moon at the Great Hall of the People in Beijing, China, May 15, 2018. REUTERS/Thomas Peter/Pool

Chinese President Xi Jinping meets head of the International Olympic Committee's ethics commission, former UN Secretary-General Ban Ki-moon at the Great Hall of the People in Beijing, China, May 15, 2018. REUTERS/Thomas Peter/Pool

Head of the International Olympic Committee's ethics commission, former UN Secretary-General Ban Ki-moon meets Chinese President Xi Jinping (not pictured) at the Great Hall of the People in Beijing, China, May 15, 2018. REUTERS/Thomas Peter/Pool

IOC President Thomas Bach speaks with former U.N. Secretary-General Ban Ki-moon as they attend the President's Dinner on the eve of the Opening Ceremony for the Pyeongchang 2018 Winter Olympics in Pyeongchang, South Korea, February 8, 2018. REUTERS/Eric Gaillard

IOC President Thomas Bach, his wife Claudia, former U.N. Secretary-General Ban Ki-moon and his wife Yoo Soon-taek pose at the President's Dinner on the eve of the Opening Ceremony for the Pyeongchang 2018 Winter Olympics in Pyeongchang, South Korea February 8, 2018. REUTERS/Eric Gaillard

Members of the Elder group, former Secretary-Generals of the United Nations Kofi Annan (L) and Ban Ki-moon (R) sit across from France's President Emmanuel Macron at the Elysee Palace in Paris, France, December 11, 2017. REUTERS/Michel Euler/Pool

L-R, Director General of the World Health Organisation, Dr. Gro Harlem Brundtland, Kofi Annan, former United Nations Secretary-General, Chair of the Elders, former Irish President Mary Robinson, Lakhdar Brahimi, a former UN-Arab League Envoy to Syria, and former UN Secretary-General Ban Ki-moon leave after a meeting at the Elysee Palace in Paris, France, December 11, 2017. REUTERS/Gonzalo Fuentes

L-R, Director General of the World Health Organisation, Dr. Gro Harlem Brundtland, Kofi Annan, former United Nations Secretary-General, Chair of the Elders, former Irish President Mary Robinson, Lakhdar Brahimi, a former UN-Arab League Envoy to Syria, and former UN Secretary-General Ban Ki-moon leave after a meeting at the Elysee Palace in Paris, France, December 11, 2017. REUTERS/Gonzalo Fuentes

Newly elected head of the International Olympic Committee's ethics commission, former UN Secretary-General Ban Ki-moon speaks during the 131st IOC session in Lima, Peru, September 14, 2017. REUTERS/Guadalupe Pardo

Newly elected head of the International Olympic Committee's ethics commission, former UN Secretary-General Ban Ki-moon speaks during the 131st IOC session in Lima, Peru, September 14, 2017. REUTERS/Guadalupe Pardo

Newly elected head of the International Olympic Committee's ethics commission, former UN Secretary-General Ban Ki-moon speaks during the 131st IOC session in Lima, Peru, September 14, 2017. REUTERS/Guadalupe Pardo

Newly elected head of the International Olympic Committee's ethics commission, former UN Secretary-General Ban Ki-moon attends the 131st IOC session in Lima, Peru, September 14, 2017. REUTERS/Guadalupe Pardo

Peru's President Pedro Pablo Kuczynski and former UN Secretary-General Ban Ki-moon pose for picture during the 131st IOC session in Lima, Peru, September 14, 2017. REUTERS/Guadalupe Pardo

Peru's President Pedro Pablo Kuczynski, International Olympic Committee (IOC) President Thomas Bach and former UN Secretary-General Ban Ki-moon pose for picture during the 131st IOC session in Lima, Peru, September 14, 2017. REUTERS/Guadalupe Pardo

International Olympic Committee (IOC) President Thomas Bach and former UN Secretary-General Ban Ki-moon pose for picture during the 131st IOC session in Lima, Peru, September 14, 2017. REUTERS/Guadalupe Pardo

French President Emmanuel Macron (C) stands with former French foreign minister Laurent Fabius (L) and former UN Secretary-General Ban Ki-moon as they attend the 'World Environment Pact' meeting at the Sorbonne where he promised to play an active role in a campaign aimed at securing a global pact to protect the human right to a clean and healthy environment in Paris, France, June 24, 2017. REUTERS/Etienne Laurent/Pool

French President Emmanuel Macron (C) stands with former French foreign minister Laurent Fabius (L) and former UN Secretary-General Ban Ki-moon as they attend the 'World Environment Pact' meeting at the Sorbonne where he promised to play an active role in a campaign aimed at securing a global pact to protect the human right to a clean and healthy environment in Paris, France, June 24, 2017. REUTERS/Etienne Laurent/Pool

FILE PHOTO - Former U.N. secretary-general Ban Ki-moon attends a media roundtable in Seoul, South Korea, January 25, 2017. REUTERS/Kim Hong-Ji/File Photo TPX IMAGES OF THE DAY

Former U.N. Secretary-General Ban Ki-moon speaks during his news conference in Seoul, South Korea January 31, 2017. REUTERS/Kim Hong-Ji

Former U.N. Secretary-General Ban Ki-moon speaks during his news conference in Seoul, South Korea January 31, 2017. REUTERS/Kim Hong-Ji

Former U.N. Secretary-General Ban Ki-moon speaks during his news conference in Seoul, South Korea January 31, 2017. REUTERS/Kim Hong-Ji

Former U.N. Secretary-General Ban Ki-moon speaks during his news conference in Seoul, South Korea January 31, 2017. REUTERS/Kim Hong-Ji

Audience watch a TV broadcasting former U.N. secretary-general Ban Ki-moon at a media roundtable, outside the venue in Seoul, South Korea, January 25, 2017. REUTERS/Kim Hong-Ji

Former U.N. secretary-general Ban Ki-moon is escorted by his bodyguards upon his arrival at a media roundtable in Seoul, South Korea, January 25, 2017. REUTERS/Kim Hong-Ji

Former U.N. secretary-general Ban Ki-moon attends a media roundtable in Seoul, South Korea, January 25, 2017. REUTERS/Kim Hong-Ji

Former U.N. secretary-general Ban Ki-moon speaks at a media roundtable in Seoul, South Korea, January 25, 2017. REUTERS/Kim Hong-Ji

Former U.N. secretary-general Ban Ki-moon attends a media roundtable in Seoul, South Korea, January 25, 2017. REUTERS/Kim Hong-Ji TPX IMAGES OF THE DAY

Joo Hyun Bahn (L), a nephew of former U.N. Secretary-General Ban Ki-moon, leaves a hearing in the federal court in Manhattan with his lawyer, Julia Gatto in New York City, New York, U.S. January 20, 2017. REUTERS/Nate Raymond

Joo Hyun Bahn (L), a nephew of former U.N. Secretary-General Ban Ki-moon, leaves a hearing in the federal court in Manhattan with his lawyer, Julia Gatto in New York City, New York, U.S. January 20, 201. REUTERS/Nate Raymond

Former U.N. secretary-general Ban Ki-moon burns incense during his visits to the natioanl cemetery in Seoul, South Korea, January 13, 2017. REUTERS/Kim Hong-Ji

Former U.N. secretary-general Ban Ki-moon and his wife Yoo Soon-taek pay a tribute at the natioanl cemetery in Seoul, South Korea, January 13, 2017. REUTERS/Kim Hong-Ji

Former U.N. secretary-general Ban Ki-moon pays a tribute at the natioanl cemetery in Seoul, South Korea, January 13, 2017. REUTERS/Kim Hong-Ji

Former U.N. secretary-general Ban Ki-moon leaves after paying a tribute at the natioanl cemetery in Seoul, South Korea, January 13, 2017. REUTERS/Kim Hong-Ji

Former UN chief Ban Ki-moon kisses a boy upon his arrival at the Incheon International Airport in Incheon, South Korea, January 12, 2017. REUTERS/Kim Hong-Ji

Former UN chief Ban Ki-moon speaks during a news conference upon his arrival at the Incheon International Airport in Incheon, South Korea, January 12, 2017. REUTERS/Kim Hong-Ji

Former UN chief Ban Ki-moon waves to his supporters as he leaves after a news conference at the Incheon International Airport in Incheon, South Korea, January 12, 2017. REUTERS/Kim Hong-Ji

Former UN chief Ban Ki-moon waves to his supporters as he leaves after a news conference at the Incheon International Airport in Incheon, South Korea, January 12, 2017. REUTERS/Kim Hong-Ji

Former UN chief Ban Ki-moon waves to his supporters upon his arrival at the Incheon International Airport in Incheon, South Korea, January 12, 2017. REUTERS/Kim Hong-Ji