Trump admitted he did not know whether Kim would spurn his advances, delivered via Twitter. "When I put out the social media notification, if he didn't show up, the press was going to make me look very bad," the US president said.
"So you made us both look good," he told Kim.
In historic first, Donald Trump steps into North Korea
The optics of their DMZ dalliance stood in sharp contrast to the made-for-TV blockbusters in Singapore and Hanoi, where everything was precisely arranged down to the last detail.
At their first encounter in Singapore, they emerged from two wings of a stage at precisely the same moment, meeting exactly in the middle for the historic handshake in front of equal numbers of North Korean and US flags.
But Trump insisted he thought of getting together with Kim only on Saturday, when his online invitation for the Panmunjom powwow electrified the G20 summit in Japan.
For his part, Kim admitted he was "surprised" by the tweet and a subsequent more formal invitation.
In the event, no one seemed sure when the two leaders should start their walks to the border.
Someone peeked out from Freedom House on the southern side, appearing to raise their hand to the north and hastily retreating.
A few seconds later Trump emerged from the glass doors while Kim, in his trademark Mao suit, advanced from the steps of Panmungak, an imposing building on the northern side.
But despite Trump's visible efforts to walk as slowly as possible he arrived on the line several seconds before Kim.
With another historic handshake, then some gesticulation from the US president, apparently pointing to North Korean soil before he took his leap into history, becoming the first occupant of the White House to set foot in the North.
Under a travel ban imposed by his administration, ordinary US citizens are not allowed to journey to the isolated country without special dispensation.
They clasped hands again on the Pyongyang side, as five North Korean photographers and cameramen buzzed around them frantically - frequently spoiling the view for snappers on the southern side, much to their frustration.
"Move! Clear! Hey! Get the photographers out the way," journalists screamed, throwing in a few expletives as the North Korean media stepped into their shot at history.
Even that high point was up in the air until the last moment, according to the US President.
"I said: 'Would you like me to come across?'" Trump said. "He said: 'I would be honoured'. I did not really know what he was going to say."
On the southern side, Trump whispered into Kim's ear - making the North Korean leader burst out laughing - before they met South Korean President Moon Jae-in, arguably the matchmaker in their unlikely bromance, as reporters jostled and hollered questions.
Trump, Kim exchanged 12 letters: S Korea minister
Trump had initially said it would be a brief handshake to "say hello" and had said it could be as short as "two minutes."
But the pair remained locked behind closed doors for nearly an hour, emerging with an agreement to direct their officials to push ahead with negotiations over Pyongyang's nuclear programme.
In the end, it was anything but a brief encounter.
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