Defense Secretary James Mattis James Norman MattisBiden courts veterans amid fallout from Trump military controversies Trump says he wanted to take out Syria's Assad but Mattis opposed it Gary Cohn: 'I haven't made up my mind' on vote for president in November MORE received incoming White House national security adviser John Bolton at the Pentagon on Thursday, and joked that he heard Bolton was "the devil incarnate."

"Mr. Secretary, it's so good to see you. Thank you for inviting me over," Bolton told Mattis upon his arrival, as captured by reporters' microphones.

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“Thank you for coming. It's good to finally meet you. I heard you’re actually the devil incarnate, and I wanted to meet you," Mattis joked.

President Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE announced last week that Bolton would be replacing national security adviser H.R. McMaster.

I am pleased to announce that, effective 4/9/18, @AmbJohnBolton will be my new National Security Advisor. I am very thankful for the service of General H.R. McMaster who has done an outstanding job & will always remain my friend. There will be an official contact handover on 4/9. — Donald J. Trump (@realDonaldTrump) March 22, 2018

Bolton previously served as United Nations ambassador and the undersecretary of State for arms control and international affairs. He was most recently an analyst at Fox News.

He is often a target for the political left, due to his hawkish, conservative views.

Bolton has suggested the possibility of a preemptive attack on North Korea to eliminate its nuclear arsenal, a position Mattis strongly opposes.

Former President Carter slammed Bolton's appointment on Monday, saying it was "the worst mistake" Trump has made in office so far.

“I have been concerned at some of the things he's decided. I think his last choice for national security adviser was very ill-advised. I think John Bolton has been the worst mistake he's made,” Carter said.