Here's how Mattis reacted to Flynn's resignation

When asked about the recent resignation of President Donald Trump’s national security adviser, Michael Flynn, Defense Secretary James Mattis sounded unmoved about Flynn’s departure.

“Here’s the bottom line, ladies and gentlemen. I’m brought in to be the secretary of defense. I give the president advice on the use of military force,” he said, according to Yahoo News Washington correspondent Olivier Knox.

Related: 5 possible replacements for Michael Flynn as national security adviser

“I maintain good relations, strong relations … and so military-to-military relations with other ministries of defense around the world,” he added.

“And frankly, this has no impact. Obviously, I haven’t changed what I’m heading there for. It doesn’t change my message at all. And who’s on the president’s staff is who I will work with.”

Mattis spoke after arriving in Brussels for a NATO meeting. Speaking with the press upon his arrival, he was reluctant to take many questions about Flynn resignation, according to Washington Post correspondent Dan Lamothe.

Flynn and Mattis have a history.

Former US National Security Advisor Michael Flynn. | via Flickr

From August 2010 to March 2013, Mattis, then a Marine general, led an investigation into unauthorized disclosures of classified information allegedly made by Flynn, who was then a lieutenant general in the US Army.

The investigation found Flynn shared “classified information with various foreign military officers and/or officials in Afghanistan without proper authorization,” according to a Washington Post report late last year. Sources told The Post the secrets were about CIA operations in Afghanistan.

Flynn was not disciplined for the incident, however, since the disclosures were not “done knowingly” and not damaging to national security.

The 26th Secretary of Defense, James Mattis, is greeted on his first full day in the position by Chairman of the Joint Chiefs of Staff, Gen. Joseph F. Dunford Jr., in Arlington, VA, Jan. 21, 2017. DoD photo by D. Myles Cullen (released)

After the investigation, Flynn was assigned to lead the Defense Intelligence Agency in September 2011. However, he was forced out of that role in early 2014, reportedly due to mismanagement.

In November, NBC News reported that Flynn personally crossed Mattis’ name off a list of candidates for national-security positions in the Trump administration.