Former Trump White House chief of staff John Kelly played up to Donald Trump’s vanity to defuse tensions between the former president and North Korean despot Kim Jong Un, according to New York Times reporter Michael Schmidt.

Trump’s insulting rhetoric about Kim was “out of control” when former four-star Marine Gen. Kelly first joined the Trump administration in 2017, Schmidt told MSNBC’s Nicolle Wallace on Thursday.

Kelly was “incredibly worried” about Trump “publicly goading Kim into war,” Schmidt continued, noting how the then-president wasn’t moved by his chief of staff’s warnings about mass deaths in North Korea or the potential tanking of its economy.

Trump only softened on Kim when Kelly, per Schmidt, said: “Look, Why don’t you become his friend? No one in American history has done that. You say all this stuff about what a great dealmaker you are, why don’t you try do that?”

“Kelly knew it would never lead to a denuclearized North Korea but he knew it would ratchet back the public and private rhetoric coming out of Trump’s mouth that could easily spin out of control,” the journalist told Wallace.

“It was only through Kelly, saying to Trump, ‘You can be the deal maker. Go all the way back to Eisenhower. No one has done this. You can do this.’ And Trump goes along with it,” he added.

Schmidt details the cause of Trump’s change of tone on Kim in the updated paperback edition of his book, “Donald Trump V. The United States,” writing how Trump had also suggested nuking North Korea and trying to place the blame elsewhere.

The “about-face between the rhetoric and the love letters” was “one of these mysteries of the Trump administration,” he said.