Updated at 2:10 p.m: Revised to include President Donald Trump's comments that Rex Tillerson is "dumb as a rock" and "lazy as hell."

WASHINGTON — President Donald Trump on Friday called Rex Tillerson, his former secretary of state, "dumb as a rock" and "lazy as hell" after the Texan criticized him as an "undisciplined" leader who "doesn't like to read" and can't grasp legal limits.

"I couldn't get rid of him fast enough," the president wrote on Twitter, using the occasion to also make clear that he was "very proud" of Tillerson's replacement, Mike Pompeo.

The dueling digs formed the latest bizarre chapter in the duo's relationship, one that started with promise over the meeting of two business minds, then soured last year amid reports that Tillerson called Trump a "moron" and finally ended in March when the president fired Tillerson by tweet.

Mike Pompeo is doing a great job, I am very proud of him. His predecessor, Rex Tillerson, didn’t have the mental capacity needed. He was dumb as a rock and I couldn’t get rid of him fast enough. He was lazy as hell. Now it is a whole new ballgame, great spirit at State! — Donald J. Trump (@realDonaldTrump) December 7, 2018

Tillerson has avoided the spotlight since he left the State Department. But that changed Thursday night when he spoke at a fundraiser in Houston for M.D. Anderson Cancer Center.

The former Exxon Mobil CEO, in comments first reported by the Houston Chronicle, gave Trump an unflinchingly dismal job review, explaining that he frequently clashed with a president who "doesn't like to get into the details of a lot of things."

"So often, the president would say, 'Here's what I want to do, and here's how I want to do it,' and I would have to say to him, 'Mr. President, I understand what you want to do, but you can't do it that way. It violates the law,'" Tillerson said.

WATCH: Former Secretary of State Rex Tillerson is speaking publicly about what led to his firing in March by President Trump.



CBS News political contributor @bobschieffer interviewed Tillerson in Houston last night, at a dinner to benefit MD Anderson Cancer Center. pic.twitter.com/47qDqcsrMs — CBS This Morning (@CBSThisMorning) December 7, 2018

Tillerson, stating the obvious, said Trump had a much different style than his own.

"He acts on his instincts and, in some respects, that looks like impulsiveness," Tillerson told the moderator, CBS News' Bob Schieffer, according to The Washington Post. "But it's not his intent to act on impulse. I think he's trying to act on his instincts."

That approach was worlds away from Tillerson's standard — the "disciplined, highly process-oriented Exxon Mobil corporation," he said.

"I didn't know how to conduct my affairs with him any other way than in a very straightforward fashion," Tillerson said, according to Politico. "And I think he grew tired of me being the guy every day that told him, 'You can't do that, and let's talk about what we can do.'"

Tillerson also lamented the effectiveness of Trump's bombastic Twitter account.

"I will be honest with you," he said, according to the Chronicle. "It troubles me that the American people seem to want to know so little about issues, that they are satisfied with 128 characters."

Trump's response Friday to Tillerson's critique was true to form.

While Trump early on had called Tillerson a "world class player and dealmaker" and "one of the truly great business leaders of the world," the president didn't hold back last year when reports emerged that his secretary of state had called him a "moron."

Even as he dismissed Tillerson's alleged insult as "fake news," he said at the time that if the diplomat "did that, I guess we'll have to compare IQ tests."

"I can tell you who is going to win," Trump said then.