Defense Secretary Jim Mattis praised outgoing U.N. Ambassador Nikki Haley Tuesday as a valued partner who has “done yeoman's work” in New York for the United States.

“She has been just a tremendous asset to those of us here in the Department of Defense,” Mattis told reporters as he awaited the arrival of the Greek minister of defense outside the Pentagon.

[READ: Nikki Haley's letter of resignation]

But Mattis would not disclose whether he knew Haley was stepping down after two years on the job.

“I don’t get into private discussions,” Mattis said.

He added that Haley’s collaborative working style will be missed. “We have a very close working relationship. We saw ourselves on many occasions collaborating together on how we would deal with certain issues alongside the secretary of state,” Mattis said. “She’s done yeoman’s work up there, and I would just tell you she may be moving on, but she’s not losing our respect one bit.”

Asked if he would be sticking around since he’s now one of the few original Trump Cabinet members left, Mattis smiled. “The team is doing very well … the beat goes on. Things are going fine.’’

Mattis last month dismissed reports that President Trump was considering replacing him after the midterm elections.