Matt Pottinger, who has served as President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE's top adviser on Asia, will serve as the new deputy national security adviser.

Newly named national security adviser Robert O'Brien confirmed the personnel move to reporters on Air Force One on Sunday while traveling to New York City with the president for the United Nations General Assembly.

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"I think Matt’s one of the most impressive young foreign policy/national defense/national security experts in the government," O'Brien said. "He’s got a wonderful personality, I think he’s a team player. He’s going to help me bring some cohesion to the [national security council]."

Pottinger has been a key figure on some of Trump's most high-profile foreign policy plays, including the summits between the president and North Korean leader Kim Jong Un Kim Jong UnNorth Korean leader Kim apologizes over killing of South Korean official Pelosi knocks Trump over refusal to commit to peaceful transfer of power Satellite images indicate North Korea preparing for massive military parade MORE. Trump and Kim have met face-to-face three times thus far, though there has been no concrete commitment to denuclearize the Korean Peninsula.

Pottinger previously worked as a correspondent at The Wall Street Journal before enlisting in the Marine Corps in 2005. He served in Iraq and Afghanistan, and joined the Trump administration in 2017.

O'Brien said a replacement for Pottinger would be announced in the near future, but that Pottinger would remain involved on Asia issues.

Trump last week announced O'Brien as his pick to replace John Bolton as national security adviser. O'Brien, who previously served as the administration's special envoy for hostage negotiations, is Trump's fourth national security adviser thus far.