Rex Tillerson has largely stayed away from the spotlight since leaving the Trump Administration in March, refusing to comment publicly about his roughly one-year stint as President Trump's secretary of state. But on Thursday, the former Exxon Mobil CEO shared a few candid thoughts about his tenure at the helm of the State Department during a charity event at the MD Anderson Cancer Center.

And Tillerson didn't pull any punches. During his talk about his time in the administration, he described Trump as undisciplined, incurious and ignorant.

Tillerson cited these factors as one reason he found it "challenging" to work in the administration (though their relationship started off strong, leaked media reports suggested that it quickly soured, culminating with Tillerson's infamous "moron" remark).

"It was challenging for me, coming from the highly processed Exxon Mobile, to go work for a man who is pretty undisciplined, doesn’t like to read, doesn’t read briefing reports, doesn't like to get to the details of a lot of things but rather says look this is what I believe."

Tillerson said he often had to explain to the president that whatever policy he wanted to pursue on that day was probably illegal.

"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,'" he said.

Unsurprisingly, word of Tillerson's criticisms (they were reported by the Houston Chronicle) quickly got back to Trump. And he was...less than pleased. So, true to form, the president issued a scathing response via Tweet late Friday, where he called Tillerson "dumb" and "lazy as hell."

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

Aside from reminding Tillerson that he still has the power to embarrass the once-mighty executive in front of the entire country, Trump's tweet also served as a pleasant distraction on a Friday afternoon when stocks - as they so often are these days - were in free-fall.