President Trump said Tuesday he is "a little disappointed" by North Korean leader Kim Jong Un's apparent change in posture after a meeting with China's president.

"There was a difference when Kim Jong Un left China the second time," said Trump at an appearance alongside South Korean President Moon Jae-in.

"I can't say that I'm happy about it."

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Earlier, Trump suggested the historic summit between himself and Kim "may not work out" amid threats from the rogue regime to cancel the June 12 talks after U.S.-South Korean military exercises.

"Maybe it will happen later. You never know about deals," he said, adding that the U.S. would be willing to "guarantee [Kim's] safety" as part of a deal for denuclearization.

Trump emphasized his personal affection for Chinese President Xi Jinping, saying his trip to Beijing last year was "two of the great days of my life."

"I don't think anybody has ever been treated better in China ever in their history," he told reporters, adding the two "speak a lot."

"President Xi is a world-class poker player and I'd maybe be doing the same thing he would do. ... Maybe nothing happened and maybe it did," the president added about Kim's secret visit to China.

Watch the clip above.

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