A second son Hin who was studying small mammals in Mongolia was shot dead in August 1945 by the Chinese Army who mistook him for a Japanese operative.

In 1946 Won and his wife moved to Pyongyang where he became head of the biology department at the newly founded Kim Il Sung University.

A former student of his, Jong Jun-thaek, however became Vice Premier of the North Korean state and helped in protecting the reputation of his teacher and advancing his career.

With the end of the Korean War in July 1953, Won became a permanent member of the Supreme People's Assembly, North Korea's unicameral parliament, which was a powerful position.

[2] The youngest son, Won Pyong-oh, grew up separated from his parents in South Korea and unknown to his father, became an ornithologist of repute.

Professor Won Hong-gu had believed North Korean propaganda that the South lived in abject poverty and misery.

In 1990, talks of reconciliation between the two Koreas began and the opportunity was utilized by North Korean ideologues who made a colour feature film in 1992 on the two Wons called "[The Birds]".

Won Pyong-oh heard of his father's death only in 1978 when he attended a meeting of the International Union for Nature Conservation at Askhabad.