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(CNN) —  

Defense Secretary James Mattis decided Thursday that the best way to break the ice during his first ever meeting with President Donald Trump’s new national security adviser John Bolton was with a joke.

“I heard you’re actually the devil incarnate and I wanted to meet you,” Mattis said in an off-microphone exchange that was captured upon Bolton’s arrival at the Pentagon.

Bolton laughed and the two men entered the building.

In the days following Trump’s decision to name Bolton as the replacement for outgoing national security adviser H.R. McMaster, Mattis has been doing his best to downplay notions that he is concerned about working with the hawkish former ambassador to the United Nations despite strong indications that the two men could clash over key issues like North Korea and Iran.

Speaking publicly for the first time about the move to name Bolton, Mattis said Tuesday that he looked forward to working with the former UN ambassador and that he hoped the two men held “different world views” to avoid “group think.”

“I’ll tell you right up front, it’s going to be a partnership, we are going to go forward,” Mattis told reporters at the Pentagon.

A senior defense official told CNN on Tuesday that the Pentagon does not expect conflict at this point between Mattis and Bolton because the role of national security adviser is more of an “aggregator” than a “policy adviser.”

“We don’t see actual changes in policy” coming down the road just because Bolton is on the job, the official said, adding that while the President can always change his mind and look for a new policy, it won’t be Bolton dictating that change.

Separately, Mattis also met with CIA Director Mike Pompeo, Attorney General Jeff Sessions and Republican Sen. Lindsey Graham at the Pentagon on Thursday, according to a Pentagon official.

CNN’s Barbara Starr contributed reporting