Washington (CNN) Former White House chief of staff John Kelly said Wednesday that Lt. Col. Alexander Vindman, a key witness in President Donald Trump's impeachment inquiry, was right to raise concerns about Trump's July call to Ukraine's president, The Atlantic reported.

Kelly also believes that Vindman, who was fired from White House last week , told the truth during testimony before House investigators last fall.

"Having seen something 'questionable (in the call),' Vindman properly notified his superiors," Kelly said at an event at Drew University, according to the magazine. "When subpoenaed by Congress in the House impeachment hearings, Vindman complied and told the truth."

"He did exactly what we teach them to do from cradle to grave," he said, according to the magazine. "He went and told his boss what he just heard."

Kelly said that when Vindman heard Trump tell Ukrainian President Volodymyr Zelensky that he wanted the country to investigate former Vice President Joe Biden and his son, Hunter, the ask was for the aide "tantamount to hearing 'an illegal order,'" The Atlantic reported. Trump and his allies have repeatedly made unfounded and false claims to allege that the Bidens acted corruptly in Ukraine.

"We teach them, 'Don't follow an illegal order. And if you're ever given one, you'll raise it to whoever gives it to you that this is an illegal order, and then tell your boss,'" Kelly said, according to the magazine.

The comments by Kelly, a retired Marine general who left the White House in January 2019, come as Trump has suggested Vindman could face disciplinary action , though a US defense official with knowledge of the matter told CNN there is no Army investigation into the Iraq War veteran and Purple Heart recipient. Although Kelly has previously voiced criticism of Trump since leaving the White House last year, he touched upon a wide array of subjects in the new interview and prompted a Twitter blast from the President later Thursday morning.

"When I terminated John Kelly, which I couldn't do fast enough, he knew full well that he was way over his head. Being Chief of Staff just wasn't for him. He came in with a bang, went out with a whimper, but like so many X's, he misses the action & just can't keep his mouth shut," Trump tweeted.

White House press secretary Stephanie Grisham called Kelly's comments criticizing the President "disingenuous" and said she was "disappointed" Thursday morning.

In addition to heaping praise on Vindman for his conduct during Wednesday night's 75-minute question-and-answer session, Kelly offered a litany of "misgivings" about his former boss, according to The Atlantic. He reportedly took issue with Trump's characterization in 2015 of Mexican immigrants as "rapists" and criminals, telling attendees that "it's wrong to characterize them that way." He also cast doubt on Trump's attempts to get North Korea to denuclearize, saying he "never did think (Kim Jong Un) would do anything other than play us for a while."

Kelly said during the event that he does not think the press is "the enemy of the people," as Trump has repeatedly claimed, according to both The Atlantic and the Daily Record, a New Jersey newspaper that also reported on the talk.

"The media, in my view, and I feel very strongly about this, is not the enemy of the people," he said, according to the newspaper. "We need a free media. That said, you have to be careful about what you are watching and reading, because the media has taken sides. So if you only watch Fox News, because it's reinforcing what you believe, you are not an informed citizen."

The former staffer also appeared to express regret over his decision to leave his White House post, according to the Daily Record, which reported that Kelly said: "I guess I feel bad, in a way, that I did leave, and I did know that if (Trump) didn't find someone like me that was willing not to stand up to him."

"But I stood firm and managed to get him to listen to all sorts of inputs and then he makes a decision, I knew this would happen," he said, according to the newspaper.

During the event, some protesters shouted at Kelly over the administration's now-reversed "zero tolerance" policy on the southern border and its travel ban on a number of foreign countries, Peter Nicholas, the article's author, told CNN.

The protesters were escorted out, though "Kelly handled it well, watching and in some cases trying to answer them," Nicholas said.

Last month, Kelly said he believes John Bolton's allegation that Trump told the former national security adviser that US security aid to Ukraine was conditioned on an investigation of the President's political rivals, adding that Bolton should be heard from. At the time, congressional Democrats were trying to get the Senate to subpoena Bolton to testify during Trump's impeachment trial but the efforts were ultimately unsuccessful.

In October, Kelly said the President would not be in the middle of an impeachment process if he were still chief of staff, implying that White House advisers could have prevented it. He also said before he left the White House he advised Trump on hiring his replacement.

"I said whatever you do, don't hire a 'yes man,' someone who won't tell you the truth — don't do that," Kelly said at the time. "Because if you do, I believe you will be impeached."