The Supreme Leader, 40, is understood to suffer from high blood pressure and diabetes, clocking in at more than 20st despite being just 5ft 5ins.

His dad Kim Jong-il died from a heart attack in 2011, and his grandfather Kim Il-sung was killed by sudden cardiac arrest in 1994.

But despite his apparent ailing health, it seems Kim has yet to pick who will take over when he dies.

In the running is understood to be his daughter, Kim Ju-ae, his notorious sister Kim Yo-jong, or the eldest son he is claimed to have.

Ju-ae – thought to be 11 or 12 – appears to be undergoing successor training, having been pictured with her dad at missile tests and military parades.

But for years, Kim’s powerful sister has been tipped as his successor and has long worked closely with her brother.

Experts believe, however, Yo-jong may not be a direct heir and could instead be appointed leader in an interim capacity if Ju-ae is too young to take the reins.

Thought of as one of the most dangerous women in the world, Yo-jong has been known to order executions.

Both she and Ju-ae have been seen publicly by Kim’s side – but a third contender, Kim’s alleged son, is cloaked in mystery.

Rumours have persisted for years that Kim welcomed a son in 2010 – yet nothing is known about him.

Dr Adam Zulawnik, senior tutor of Korean Studies at the University of Melbourne, previously told The Sun: “Whether or not Kim has an eldest son has, in itself, been debated, with some theories indicating that he could be rearing him behind the scenes as a successor.

“This is based on the assumption that North Korea would follow a Confucian patriarchal model of male succession. Another possibility,  however, is that Kim’s eldest son is somehow unsuitable for succession.

“This could be due to any number of reasons, ranging from the individual not being interested or even health issues.

“Mental health and developmental issues, in particular, are still highly stigmatised in many parts of the world, and so any learning disability would likely be enough to rule out succession.”

Dr Zulawnik believes that if Kim Ju-ae becomes leader, the only plausible explanation would be that the son does not actually exist or is not suitable.