Secretary of Defense James Mattis' first-ever meeting with John Bolton, President Trump's latest pick for national security adviser, started off with a laugh as the secretary joked that he had heard Bolton is the "devil incarnate."

"Ambassador Bolton, so good to see you. Thanks for coming and it's good to finally meet you. I heard that you're actually the devil incarnate and I wanted to meet you," the secretary can be heard saying in an off-mic moment while greeting the former Ambassador to the United Nations. Bolton laughed off the remark as the two entered the Pentagon for their official meeting.

The meeting was the first for the two as Bolton is set to officially replace Lt. Gen. H.R. McMaster as national security adviser on April 9.

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Speculation concerning Bolton's ability to work well with Mattis has circulated in recent weeks. Bolton, a noted hawk, has argued for military intervention against North Korea as well as completely abandoning the Iran nuclear deal.

Mattis, however, has tried to dispel concerns about their working relationship, saying he was confident in a "partnership" developing between the two.

"He's going to come over this week. Last time I checked he's an American. I can work with an American," Mattis told reporters last week.

According to CBS News' David Martin, after his meeting with Mattis, Bolton was expected to also meet with Chairman of the Joint Chiefs of Staff Gen. Joseph Dunford.

Mr. Trump tweeted about the staff shakeup late last week, saying that he was "very thankful for the service of General H.R. McMaster who has done an outstanding job & will always remain my friend."