North Korean dictator Kim Jong-un's powerful uncle could be the next in line as the ruthless regime may never accept a woman as leader.

Kim Pyong-il – the half brother of previous leader Kim Jong-il – has recently returned to the secretive state after spending 30 years living overseas as a diplomat.

With ongoing rumours of Kim Jong-un's death or failing health, experts have said his uncle's re-emergence on the stage of North Korean politics could complicate the succession – with Kim Jong-un's sister Kim Yo-jong believed to be the next in line.

Kim Pyong-il was considered a threat even by his older brother, which is one of the reasons he spent so long abroad – being North Korea's ambassador to Finland, Bulgaria, Hungary and Poland.

Reportedly he was once considered to rule alongside Kim Jong-il by their dad Kim Il-sung, potentially being made head of the military while his brother took over the party.

media_camera Kim Yo-jong with her brother, North Korean leader Kim Jong-un. Picture: Pyongyang Press Corps Pool via AP

He is said to have been a popular figure in Pyongyang before his apparent exile – known for hosting parties where people would chant his name.

China are also reportedly keen on Kim Pyong-il, considering him an alternative should regime change occur in North Korea.

The 65-year-old returned to Pyongyang last summer after retiring as a diplomat and is reportedly popular due to his resemblance to his dad Kim Il-sung.

North Korean society is built upon a cult of personality around the Kims, and something seemingly as trivial as appearance may go a long way with the kingmakers in the regime.

Meanwhile, Kim Yo-jong has been positioned as Kim Jong-un’s “alter ego” in recent years, taking an increasingly prominent position alongside her brother.

It is possible Kim Jong-un’s death could spark a brutal Game of Thrones-esque conflict to establish his successor.

North Korea, however, today released a letter said to be written by Kim Jong-un – but no new pictures – as the mystery deepens.

Professor John Blaxland, an expert on North Korea, said Kim Pyong-il's gender may make him a preferable choice over his niece.

He told ABC: “It's a fascinating development to see Kim Pyong-il re-emerge on the stage.

“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.”

Dr Malcolm Davis, from Australia's Strategic Policy Institute, added: “Kim Yo-jong is clearly likely to claim leadership … but whether the North Korean factions will accept a female leader … is uncertain.”

media_camera North Korean dictator Kim Jong-un's powerful uncle could be the next in line as the ruthless regime may never accept a woman as leader. Picture: Korea News Service via AP

Other experts have, however, disagreed that sexism may play a role in stopping Kim Yo-jong's ascension.

North Korea expert Sean King said any leader must be a blood relative, and currently Kim Yo-jong was in pole position.

The 32-year-old is one of her brother's closest aides, helped cultivate his image and played a key role in Kim Jong-un’s historic meetings with US President Donald Trump.

Mr King 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.”

Kim Jong-un does have children, but they are currently far too young to rule.

Kim Jong-un has not been seen in public since April 11, and rumours are running wild on his possible demise.

Reports from the US, China, South Korea and Japan have speculated there is something wrong with the North Korean leader – including a botched heart surgery, an injury during a missile test or a collapse while walking in the countryside.

Chinese journalist Shijian Xingzou said a “very solid source” told her the North Korean leader had died.

She has 15 million followers on Chinese social media site Weibo, and she is also the niece of one of the country's foreign ministers.

South Korea have, however, insisted that Kim Jong-un is “alive and well”, and other reports have suggested his vanishing is down to him weathering the coronavirus storm at his private resort in Wonsan.

Mr Trump has said he believed the reports were “incorrect”, but then one of his advisers told Fox News that Kim Jong-un was most likely dead or incapacitated.

Kim's health has long been in question – with the dictator believed to be a binge eater, heavy drinker and chain smoker potentially weighing up to 127kg.

Pictures have also emerged allegedly showing Kim Jong-un lying in state, but these have been faked based on images from his dad's funeral in 2011.

– This article originally appeared on The Sun and was reproduced with permission

Originally published as Why Kim’s sister won’t be next leader