A retired general has branded Jim Mattis's attack on President Trump as "totally unprofessional."

Mark Hertling, a lieutenant general who spent 37 years in the U.S. Army, slammed Mattis for his jabs at the president during his address at Thursday night's white-tie Al Smith Dinner.

"I thought [the jokes were] totally unprofessional and uncalled for, and it’s not something a professional military member should do in my view," Hertling said on CNN. "I don’t think I’ve ever actually insulted the man as the president. And that’s unfortunately what Secretary Mattis did last night. It was insulting. That’s why I consider it unprofessional."

"The young folks in our military are constantly debating now more than I’ve ever seen them do this, there is an active discussion going on with the junior leaders about the civil military-relationship. And in the time of Trump, it is deteriorated to a degree where it’s causing divisions in the military as well. And that’s unfortunate because the military is a professional body that takes an oath to defend the Constitution," he continued.

During Mattis's speech, he said he was "honored" to be considered the "most overrated general" because he "also called Meryl Streep an overrated actress. So I guess I'm the Meryl Streep of generals, and frankly, that sounds pretty good to me." He also took shots at the president for deferring on military duty during the Vietnam War, citing bone spurs.