(CNN) -- In 2001, the North Korean regime, then headed by Kim Jong Il, was dealt an embarrassing if minor setback.
The leader's son, Kim Jong Nam, was caught sneaking into Japan on a fake diplomatic passport -- so that he could visit Tokyo Disneyland.
His choice of destination wasn't the only reason for red faces in Pyongyang.
More pertinently, it was that he had exposed that members of the regime used fake passports to travel overseas, according to Michael Madden, a frequent contributor to North Korean monitoring organization 38 North and visiting scholar at the US-Korea Institute at Johns Hopkins University.
It was a rare window into the workings of the North Korean elite, seen through the prism of former leader Kim Jong Il's first-born son, an overweight playboy, but also a smart and open-minded man, according to Yoji Gomi, the author of the 2012 book "My Father, Kim Jong Il, and Me." Gomi interviewed Kim for the book.
Kim Jong Nam was born in 1971, the result of an affair between Kim Jong Il and North Korean actress Song Hye-rim, said Madden. The affair has been widely reported by international media.
She was married at the time, though was later compelled to get a divorce, said Madden, who has researched Kim through contact with people who knew him, as well as fellow North Korea watchers and other experts.
Because of the conservatism of North Korean society, their illegitimate child was hidden from both the public and, initially, his grandfather, Kim Il Sung, the founder of the DPRK, an acronym the regime uses for North Korea, Madden said.
"Kim Jong Il had a standing order to execute anyone who talked about his private life," Madden said. "North Korea is very conservative so (for people) to hear the news that he had many children from different women would have been tawdry."
Kim Jong Il's sister, Kim Kyung Hee attempted to adopt the baby shortly after he was born but was overruled. She did remain close to her nephew for the remainder of her life, Madden said.
While his father doted on him in secret, he was persuaded to send Kim Jong Nam overseas for his education.
In the late 70s, Kim Jong Nam started studying in Geneva, but was later moved to Moscow, which was seen as ideologically more suitable, according to Madden. However, he was later completed his schooling in Geneva.
In the meantime, Kim Jong Il had started a relationship with a dancer from a dance troupe called Ko Yong Hui, who would later give birth to three children, one of whom was his half-brother and future leader of the country, Kim Jong Un, Madden said.
Madden said Kim Jong Nam resented the fact that his father had started a new family.
Upon his return to Pyongyang, the rebellious teen was said to have resented having to live behind palace gates, a lifestyle very much unlike that in Switzerland.
He was close with his paternal aunt, Kim Kyung Hee, and her husband, Jang Song Thaek, who was one of the few people that knew everything about Kim Jong Il, his brother-in-law.
Jang's execution, ordered by Kim Jong Un in late 2013, would have affected Kim Jong Nam "badly," Madden said.
Relationship with his half-brother
Brought up by different families, with a 13-year age gap and an extended absence by Kim Jong Nam, Madden said there was "no chance in hell they were raised together in any way."
Gomi, the author of the 2012 book, said that the two brothers never even met because of the ancient practice of raising potential successors separately.
The house that Kim Jong Nam grew up, a residence in the Worker's Party headquarters, was demolished in 2009 or 2010, and is now is the site of the Kim Jong Un's official residence.
"There's symbolism there, that they wrecked his childhood home," Madden said. "It was the house that he used when he went back to North Korea."
Kim Jong Un's mother, Ko Yong Hui, was politically ambitious and, through befriending members of her common-law husband's inner circle, positioned her sons in the line of succession, Madden said.
Out of the picture as his father's successor, Kim Jong Nam nevertheless maintained a role within the North Korean regime. He was said to have led a network of people who worked for Kim Jong Il, managing accounts worth millions of dollars, and checking up on diplomats.
Kim told Japan's TV Asahi in 2010 that he opposed his family holding onto power for another generation, but had "no objection nor interest" in the matter.
He spent much of his time outside of North Korea -- he had residences in China, specifically the former Portuguese enclave and Special Administrative Region of Macau. He was "more or less exiled" there, Denny Roy, a North Korea analyst at the East-West Center in Honolulu told CNN in 2011.
Son's 'isolated' life
In a 2012 interview, Kim's son, Kim Han Sol, spoke of having few friends in North Korea before moving to Macau.
"When I was growing up it was very isolated, first of all to keep it very low profile," his son, Kim Han Sol, told former UN Under-Secretary General Elisabeth Rehn in an interview for Finnish televison.
"That's why I didn't really have (many) childhood friends from North Korea. That's why all my friends are from outside, such as Macau."
In the Rehn interview, Kim Han Sol said he usually visits the reclusive country every year to meet relatives.
"Kim Jong Nam routinely interacts with (South Korean) tourists visiting China, and gives occasional media interviews," Madden writes on his blog, NK Leadership Watch.
Madden also says that he had ties to "numerous personal and social ties to DPRK elites" as well as the sons of former Chinese President Jiang Zemin.
He reportedly has at least three children, according to South Korean media, the only known grandchildren of Kim Jong Il, who passed away in 2011.
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