Former Secretary of State Rex Tillerson laid out parts of his version of what went wrong in his relationship with President Donald Trump, saying he and the president don’t “have a common value system” and describing scenarios where he had to curtail Trump’s impulses because “it violates the law.”

Tillerson, who was fired in March, made his first public appearance in months at a Houston fundraiser on Thursday. He sat down for an interview with CBS News veteran Bob Schieffer at the event and discussed his time at the State Department under Trump.

Tillerson said that he had never met Trump “until the day he asked me to be secretary of state” and described his impressions of the president.

“He acts on his instincts,” Tillerson said. “In some respects, that looks like impulsiveness, but it’s not his intent to act on impulse. I think he really is trying to act on his instincts.”

Prior to becoming secretary of state, Tillerson was the longtime CEO of oil and gas giant ExxonMobil. He told Schieffer that coming to the Trump administration from the “disciplined, highly process-oriented” Exxon was “challenging” — and seemed to take some shots at Trump. He said the president “doesn’t like to read,” including briefing reports, and “doesn’t like to get into the details of a lot of things.”

He said Trump says, “Look, this is what I believe. And you can try to convince me otherwise, but most of the time, you’re not going to do that.”

Schieffer then asked Tillerson what he thinks caused his relationship with Trump to go off the rails. Tillerson was candid in his response:

Part of it was obviously we are starkly different in our styles. We did not have a common value system. When the president would say, “Here’s what I want to do, and here’s how I want to do it.” And I’d 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. It violates treaty.” He got really frustrated. I didn’t know how to conduct my affairs with him any other way than in a very straightforward fashion, 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.”

Schieffer responded, “That’s very, very interesting,” and the audience laughed.

Tillerson did not indicate in what aspects he believed Trump tried to violate the law.

Former Secretary of State Rex Tillerson tells @CBSNews' @bobschieffer that he and President Trump "Did not have a common value system ... I'd have to say to him, 'Mr. President, I understand what you want to do, but you can't do it that way .. You know, he got really frustrated." pic.twitter.com/oI8ocQUJni — Norah O'Donnell (@NorahODonnell) December 7, 2018

Rex Tillerson was perhaps an adult in the room. But he also did a lot of damage at the State Department.

Tillerson, during his tenure, was supposed to be one of the “adults in the room” guiding and tempering the volatile Trump, much like Defense Secretary Jim Mattis or now-former National Security Adviser H.R. McMaster and National Economic Council Director Gary Cohn.

Before Trump fired him, the pair reportedly clashed often — Tillerson argued for the president to stay in the Paris climate agreement and pushed him to certify Iranian compliance with the Iran nuclear deal. And Trump wasn’t shy about making their disagreements public at times.

I told Rex Tillerson, our wonderful Secretary of State, that he is wasting his time trying to negotiate with Little Rocket Man... — Donald J. Trump (@realDonaldTrump) October 1, 2017

...Save your energy Rex, we'll do what has to be done! — Donald J. Trump (@realDonaldTrump) October 1, 2017

But it’s not as though Tillerson was a resounding success as secretary of state. Perhaps he tempered Trump on some things, but as Vox’s Zack Beauchamp explained earlier this year, he left his post without any major accomplishments, and did a lot of damage to the State Department in the process:

Under Tillerson’s watch, 60 percent of State’s top-ranking career diplomats resigned and new applications to join the foreign service fell by half, according to a November count by the American Foreign Service Association. This hollowing-out of the foreign service, combined with Tillerson’s inability to appoint people to vital positions like ambassador to South Korea, delayed American responses to major crises and weakened the State Department for a “generation,” according to George Washington University’s Elizabeth Saunders.

It’s not clear whether Tillerson’s Thursday appearance is a one-time shot or marks a step back into public life where we’ll hear more about his time in the Trump administration. His remarks were relatively tempered, but it’s clear there’s not a ton of love lost between Tillerson and Trump — he was, after all, fired via tweet.