The rumour mill is in overdrive as the fate of the head of one of the world's most secretive dynasties remains a mystery.

CNN reported on April 21 that North Korea's leader Kim Jong-un was gravely unwell after surgery.

The report was dismissed by South Korea's presidential palace, which said it had received no information that suggested the 36-year-old was seriously ill.

However, as speculation continues to mount over the health of Kim Jong-un, attention is turning to who is next in line to take over in the event of his death.

"There is no clear succession process in place, and Kim is in very poor condition, so when he does die, things could get quite dangerous and messy," said Malcolm Davis, a senior analyst at Australia's Strategic Policy Institute.

Kim Yo-jong, a young, ambitious and trusted sister appears to be an obvious choice, but experts suggest there is a second dark horse candidate, and any transition of power will not be a smooth one.

Kim Jong-un must be succeeded by a blood relative

Having run the country for 70 years, the Kim family holds almost God-like status in North Korea.

Kim Yo-jong is often referred to as her brother's chief propagandist, styling him in the image of their grandfather Kim Il-sung. ( Jorge Silva/Pool Photo via AP, File Photo )

New York-based political analyst and Asian affairs specialist Sean King said any leader must be a blood relative of the Kim family.

But with older brother Kim Jong-nam assassinated in 2017 and another brother, Kim Jong-chol, an unlikely and unfavoured candidate, there is no other immediate male obvious successor in place among Kim Jong-il's children.

Young, powerful and educated, Kim Yo-jong is one of her leader brother's closest confidants.

Not only is she constantly by his side curating his image, she has also played a key role in both the US-North Korea summit and the inter-Korean summit.

"Any hypothetical successor would have to be a Kim family member. North Korea's constitution specifically mentions Kim Il-sung and Kim Jong-il," Mr King said.

"I don't think North Korea can maintain its separate existence without a Kim in command because North Korea without a Kim at the top is like Christianity without Jesus."

Information surrounding the family and their health remains a closely guarded secret.

North Korea's leader Kim Jong-un is believed to have children with wife Ri Sol-ju (centre), but sister Kim Yo-jong (left) may be his most likely successor. ( Korea Summit Press Pool/Reuters )

It is known that Kim Jong-un has at least two children, however they are far too young to rule.

"If Kim Jong-un dies before his two children are grown up enough to succeed him, most certainly a collective leadership would be appointed to rule the country before a dynastical successor is ready to take over," said Leonid Petrov, one of Australia's leading North Korea experts.

Dr Petrov, a senior lecturer at the International College of Management Sydney, warned in that scenario, the "shaky balance" between the ruling political class and the military would be lost.

"One of the factions would prevail and lead the process of political reforms, which have been overdue since the early 1990s. Reforms will lead to regime collapse and re-unification of Korea," he said.

The trusted sister who could rule North Korea

While Kim Yo-jong may be her brother's number two, Dr Petrov said the country's ideology dictates that North Korea is a revolutionary state where the Great Leader plays a paternalistic role for the nation.

This presents an obvious and potentially dangerous problem for the woman, who's believed to be about 31 years old.

"Kim Yo-jong cannot be the Great Leader and the Father of Nation," Dr Petrov said.

Some North Korea experts say Kim Yo-jong would have to battle sexist members of the country's ruling class to claim the top job. ( Kyodo via Reuters )

"Sooner or later she would be removed from her post and replaced either by a male member of the Kim clan or by the collective leadership representing the Korean Workers Party and Korean People's Army."

Dr Petrov also suggests Kim Yo-jong would struggle to give orders in North Korea, a Confucian country where seniority and masculinity are respected.

He said there was "every chance North Korea's elite may reject her".

"Kim Yo-jong is clearly likely to claim leadership … but whether the North Korean factions will accept a female leader … is uncertain," Dr Malcolm Davis said.

The powerful uncle waiting in the wings

There may be one relative who could complicate matters for Kim Yo-jong, according to Professor of International Security and Intelligence Studies at ANU, John Blaxland.

Kim Pyong-il, the half-brother of Kim Jong-il and the current leader's uncle, has returned to North Korea after years overseas as a diplomat.

Kim Pyong-il, pictured here with Polish diplomat Mariusz Handzlik, has served as North Korea's ambassador to Hungary, Bulgaria, Finland, Poland, and the Czech Republic. ( Wikimedia Commons: Chancellery of the President of the Republic of Poland )

While 65 years old and less prominent, he has the advantage of not only being a blood relation to the current leader, but also male.

"It's a fascinating development to see Kim Pyong-il re-emerge on the stage," Prof Blaxland said.

"That certainly will complicate Kim Yo-jong's apparent aspirations, but points to something that was expected: a reluctance of the establishment — military, security leaders and the Kim family — to depart from the patriarchal predisposition."

Others disagree that sexism will stand in Kim Yo-jong's way.

Mr King said Kim's younger sister has played such a pivotal role in recent times for a good reason.

"It's no accident that Kim Yo-jong has been placed front and centre as she has been," he said.

"She's clearly being groomed for something. If Kim Pyong-il was the man for the job, he'd have likely gotten it previously."

What a change at the top in Pyongyang means for the world

China, the US and South Korea, which all have a keen interest in ensuring stability on the Korea peninsula, will be closely monitoring any potential change of leadership.

Kim Yo-jong accompanied her brother to the Vietnam summit with the US in 2019. ( Reuters: Jonathan Ernst )

Dr Davis said he doubted any leadership change would be a smooth transition.

Instead it could turn into a "dangerous vacuum in which multiple factions vie for power".

Professor Blaxland said whatever happened next will ultimately depend on manoeuvres by Kim Pyong-il, his niece and their backers.

"It could be an orderly transition, but the stakes are high and the prospects of an implosion can't be completely eliminated," he said.

Professor Blaxland said that could trigger "external intervention" from South Korea or someone else.

"[South Korean President] Moon Jae-in seems keen to keep the regime in place, so that is a significant pointer in favour of their regime's survival, but also to considerable tensions between [South Korea] and the USA."

