Mount Baekdu, which straddles the China-North Korea border, is the highest and most sacred mountain on the Korean peninsula.

It is the place where North Korean founding leader Kim Il Sung fought against Japanese occupation forces, and where his son Kim Jong Il was born. Or at least that is what North Koreans are told to believe.

The so-called "Mount Baekdu bloodline" is used by the Kim family to legitimise its iron-fist rule in North Korea for the past seven decades. Sadly, the bloodline is also the most probable reason why Mr Kim Jong Nam, 45, was killed in Kuala Lumpur two weeks ago.

He is widely believed to have been assassinated on orders from his youngest brother, Mr Kim Jong Un, North Korea's current leader, who sees him as a threat to the throne.

Born to Mr Kim Jong Il and popular actress Song Hye Rim, Mr Kim Jong Nam lived a life of luxury from young. "Kim Jong Il doted on his son - sleeping with him, eating dinner and telephoning him when he was too busy to return home," said North Korean leadership expert Michael Madden, a visiting scholar at Johns Hopkins University.

Contrary to reports that Mr Kim Jong Nam fell out of favour after he was caught trying to enter Japan in 2001 using a fake passport, the father and son kept in contact until the last months that Mr Kim Jong Il was alive, Mr Madden told The Straits Times.

"As in many parent-adult child relationships, they certainly had conflicts and arguments. However, he was never cut off from contact or support from his father."

Even when he was in exile in Macau, he reportedly managed his father's slush funds, negotiated weapons deals and travelled to South-east Asia to launder money and manage the family's businesses in the region.

"Jong Nam had a trust account and earned money doing favours for his father," Mr Madden said.

Upon the death of Mr Kim Jong Il in 2011, the eldest son inherited "no small sum of money" from his father, according to the South Korean media.

He also took over the Kim family's secret accounts following the death in late 2013 of his uncle, Mr Jang Song Thaek. The former No. 2 man in North Korea, who was said to be close to the Chinese leadership, was executed - on orders from Mr Kim Jong Un - for treason after being branded "despicable human scum".

Mr Madden said that Mr Kim Jong Nam sometimes played a direct supervisory role in managing some of the Kim regime and family accounts, and sometimes, he was just an interlocutor.

These accounts were "not under the control of Kim Jong Un", said Mr Madden.

Speculation has it that Mr Kim Jong Un had ordered his half-brother Jong Nam to return to Pyongyang with all the money in order to help ease the state's financial burden due to toughened United Nations sanctions.

But Mr Kim Jong Nam refused.

He was also known to have ties with Office 39, a secretive government division which provides the ruling Kim family with billions of dollars from an array of illicit and licit businesses.

South Korean think-tank Sejong Institute's senior researcher, Dr Hong Hyun Ik, was cited as saying by Yonhap news agency that Mr Kim Jong Nam carried out deals involving North Korean weapons when he was living in China.

There were also rumours that he frequented casinos in South-east Asia to launder money, while some media reports said he indulged in gambling.

Mr Madden said he was not necessarily a high-roller, although he did enjoy slot machines, pachinko, and a variety of board and card games.

The talk is that Beijing offered protection to Mr Kim Jong Nam as an alternative heir in case his younger half-brother got dethroned.

Born to different mothers, the two brothers were raised separately and met only once - during the private funeral of their grandfather, Mr Kim Il Sung, in 1994.

North Korea expert Ken Gause, writing in the book North Korean House Of Cards, said Mr Kim Jong Il in his will and testament had "urged that Kim Jong Nam be left alone and not targeted or harassed by the regime".

In the wake of Mr Kim Jong Nam's death, attention has shifted to his firstborn child - 21-year-old Kim Han Sol. Once, during a rare TV interview in 2012, the young Kim called Mr Kim Jong Un a "dictator".

His reply to a question why his uncle was appointed as leader was: "My dad was definitely not really interested in politics.

"I really don't know how he (Mr Kim Jong Un) became a dictator... It was between him and my grandfather."

Mr Kim Han Sol, a graduate of France's prestigious Sciences Po university, also said he had not been aware of his lineage until he was much older.

"I really didn't know until later on that my grandfather was a leader in Korea...

"Little by little, through conversations my parents had, I started to put the puzzle pieces together and then I realised who he was," he told Finnish broadcaster Yle. He has never met his grandfather.

With the demise of his father, there are concerns that he might be next on the hit list.

South Korean lawmaker Lee Cheol Woo said Mr Kim Han Sol and his family are in Macau. "They are under the protection of the Chinese authorities," he said.

Beijing has neither confirmed nor denied this.