The grandfather of North Korea's leader worked as a collaborator with Japanese soldiers who were hunting Kim Il-sung during the Second World War, according to documents unearthed in Tokyo.
Kim Jung-un's maternal grandfather, Ko Gyon-tek, worked at a sewing factory in Osaka making uniforms for the Japanese army who were hunting Kim Il-sung, the guerrilla leader and founder of the North Korean regime whose son would later marry the current dictator's mother. Collaborating with the Japanese occupiers of Korea would normally have meant a long incarceration in North Korea's notorious gulags for the traitor and his family. But Mr Ko avoided that fate after he returned to North Korea in the early 1960s thanks to his daughter being in the favour of Kim Jong-il, the son of Kim Il-sung.
Ken Kato, a human rights activist who discovered the files in Japan's military archives and the library of the country's parliament, believes they undermine Kim Jung-un's legitimacy to rule. He also believes that the dictator, who is thought to be 29, will have been unaware of his grandfather's background - which would have placed him in the lowest "hostile" class of North Korean society.
Born on Jeju Island in what is now South Korea, Mr Ko moved to Japan in 1929 and was involved in a number of businesses, both legal and illegal, including people smuggling. During the war years, the factory where he worked was controlled by the Ministry of War. His daughter, Ko Young-hee, was born in Osaka in 1953, but the family was forced to move to North Korea in 1961 after her father was arrested by Japanese police for human trafficking and deported.
"People who went back to North Korea from Japan could never be in the 'core' class, according to the regime, so they would have been in the 'wavering' or 'hostile' classes," said Mr Kato.
Mr Ko apparently managed to conceal his past and found work in a chemical factory, the records indicate, while his daughter began to dance with the Mansudae Art Troupe. It was as a dancer that she caught the eye of Kim Jong-il, who was being groomed to take over North Korea. Their first child, Kim Jong-chul, was born in 1981 and Kim Jong-un followed in January 1983. His mother died in Paris in 2004, apparently of breast cancer.
While Kim Jong-il, who died last December, is almost certain to have known about the background of his wife's father, that stain on his pedigree is likely to have been concealed from the man who now rules North Korea.
"There is a strict classification system that is based on pedigree in Korea that dates back to the 6th century and is part of the culture," said Mr Kato. "According to North Korean philosophy, Kim Jong-un is not a suitable leader because the legitimacy of his entire regime is based on his pedigree," he added. "Under their rules, his family should have gone to concentration camps."
