Tokyo (CNN) -- They share the same rotund facial features, similar expressions and gait. But the two sons of Kim Jong Il have never met, and based on a new book being published in Japan this week, there appears to be little fraternal allegiance, at least from the eldest son's side.
Kim Jong Nam, the eldest son, is the half-brother of Kim Jong Un, the new leader of North Korea. Kim Jong Nam believes his youngest brother will fail as the "supreme leader" of the reclusive state, according to the book's author, Yoji Gomi.
"He's not comfortable that his younger brother is succeeding the power of Kim Jong Il," says Gomi, the author of "My Father, Kim Jong Il, and Me," which will hit bookshelves in Tokyo on Wednesday. "He (Kim Jong Nam) sees his brother failing. He thinks he (Kim Jong Un) has a lack of experience, he's too young, and he didn't have enough time to be groomed. Those three reasons are why he thinks he'll fail."
Kim Jong Nam is the most public of Kim Jong Il's sons, known primarily for his blunders and semi-exile from North Korea. An overweight and careless playboy, Kim Jong Nam enraged his father more than a decade ago when he was arrested slipping into Japan with forged documents -- simply to visit Disneyland. Kim Jong Nam lives in China and Macau and has occasionally popped up in the Japanese news media.
It was during one of those appearances in front of Japanese reporters -- in Beijing, during 2004 -- that Gomi, a reporter for the Tokyo Shimbun, first met Kim Jong Nam. They exchanged email addresses and began an occasional correspondence. In the past few years, Gomi said they had begun to write more, exchanging 150 emails. Last year, Kim Jong Nam agreed to meet with Gomi in Macau and Beijing for interviews.
What surprised Gomi the most, he said, is that the eldest of Kim Jong Il's sons was very smart and knowledgeable about the world -- and open-minded, especially about economic reforms.
"He spoke out against his father's 'military first' policy," says Gomi, countering widely held notions that the Disneyland debacle caused Kim Jong Nam to fall out of favor with his father. "He wants North Korea to embrace economic reform and open its doors."
Kim Jong Nam painted a picture of a father who was strict but was often warm-hearted to his eldest son, Gomi said, especially on special occasions. "Kim Jong Il called his son on his birthday," Gomi said.
Kim Jong Nam says the half-brothers were kept apart, following an ancient history of raising potential successors separately.
He says his father refused to discuss the succession of power for many years because it signaled his own death, according to Gomi -- only after his illness accelerated did the succession begin.
Both sons were educated in Switzerland, leaving Kim Jong Nam convinced that his country needed to embrace economic reforms. Kim Jong Nam believes his brother won't have the power to push through reforms, Gomi said.
"He's afraid the youngest son has no idea, no vision about economic reform," he said.
Professor Andrei Lankov of Kookmin University says Kim Jong Nam has been fairly public in the past, keeping his distance from the regime's inner circle. Lankov says he believes the latest comments are the reaction of a normal, intelligent human being who has a good understanding of the situation in North Korea.
"I would say maybe this smart, overweight playboy from Macau has the highest chances of physical survival of all the Kim Jong Il children," says Lankov.
"In the long run, the history of the North Korean state is going to end badly. We might see a coup, a revolution, a conspiracy, because in the very long run the system is not sustainable," Lankov said. "He (Kim Jong Nam) is away, he is secure. It is quite possible that many of his siblings will die a violent death sooner or later, and he is likely to live until an old age, writing memoirs, explaining to everybody how misunderstood his family was."