U.S. President Donald Trump shakes hands with North Korean leader Kim Jong Un at the Capella Hotel on Sentosa island in Singapore June 12, 2018. REUTERS/Jonathan Ernst 

U.S. President Donald Trump and North Korea's leader Kim Jong Un walk together before their working lunch during their summit at the Capella Hotel on the resort island of Sentosa, Singapore June 12, 2018. Picture taken June 12, 2018. REUTERS/Jonathan Ernst TPX IMAGES OF THE DAY 

South Koreans watch a television screen with news showing a picture of Kim Jong-un, North Korean leader Kim Jong-il's son, at the Seoul railway station August 26, 2010. North Korea's reclusive leader Kim is visiting China, his only powerful ally, with his son and heir apparent Kim Jong-un, a South Korean presidential source and local media said on Thursday. The Korean characters on the screen read, "Kim Jong-il suddenly visits to China. For a discussion on his heir?" REUTERS/Jo Yong-Hak (SOUTH KOREA - Tags: POLITICS MILITARY) 

South Korean President Moon Jae-in and North Korean leader Kim Jong Un shake hands at the truce village of Panmunjom inside the demilitarized zone separating the two Koreas, South Korea, April 27, 2018. Korea Summit Press Pool/Pool via Reuters TPX IMAGES OF THE DAY 

South Korean President Moon Jae-in and North Korean leader Kim Jong Un arrive for a banquet in Pyongyang, North Korea, September 18, 2018. Pyeongyang Press Corps/Pool via REUTERS 

North Korean leader Kim Jong Un and his sister Kim Yo Jong attend an opening ceremony of a newly constructed residential complex in Ryomyong street in Pyongyang, North Korea April 13, 2017. REUTERS/Damir Sagolj TPX IMAGES OF THE DAY 

North Korean leader Kim Jong Un (inside a vehicle) bids farewell to South Korean President Moon Jae-in as he leaves after a farewell ceremony at the truce village of Panmunjom inside the demilitarized zone separating the two Koreas, South Korea, April 27, 2018. Korea Summit Press Pool/Pool via Reuters TPX IMAGES OF THE DAY