Kim’s disappearance from the public eye in April led to claims that he was in a vegetative state after botched heart surgery. However, Mr Trump’s surprising tweet sought to scotch the rumours. He said: “Kim Jong Un is in good health. Never underestimate him!”
Mr Trump has met Kim on three separate occasions, and boasted earlier this year of the “beautiful letter” the Supreme Leader had sent him.
The US President’s tweet took Twitter users by surprise, with one commenting: “What the actual ****?”
There is no indication as to what prompted his post.
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Kim Jong-un was absent from the public eye for more than a fortnight before reemerging at the opeing of a fertiliser factory in Pyong Yang – although sceptics pointed out there was no way to prove when the footage was show.
The 36-year-old, who has been the country’s leader since 2011, taking charge after the death of his father, Kim Jong-il.
He is well-known for his love of rich food, and is also thought to have spent vast sums of money on imported Hennessy’s Cognac.
Speaking before Mr Trump’s tweet, Ankit Panda, author of a new book about Kim entitled Kim Jong-un and the Bomb: Survival and Deterrence in North Korea, told Express.co.uk: “Diagnosing anyone’s health status from afar is a perilous task, even for medical specialists, but it’s well known — and frankly obvious from a glance — that Kim Jong Un is not the perfect picture of health for someone his age.
“South Korean and U.S. intelligence agencies, in particular, pay close attention to this.
“The recent rounds of rumors about his death have been baseless, but remind us that one of the persistent sources of risk today in North Korea is that Kim is prematurely incapacitated before a proper succession is in place.”
Mr Panda added: “That sets up the sort of intra-system power struggle that has been known to take place in other monolithic authoritarian systems.
“In the end, we’ll likely be left with very little good information about Kim Jong Un’s vital statistics and overall health status, but it behooves us to take the matter seriously.”
(More to follow)