Nine months after being fired by President Trump, former Secretary of State Rex Tillerson has some pretty unflattering things to say about his old boss.

Tillerson spoke with CBS News on Thursday and said it was "challenging ... to go to work for a man who is pretty undisciplined, doesn't like to read, doesn't read briefing reports, doesn't like to get into the details of a lot of things." He also suggested that during his tenure, he was often stepping in to tell Trump that the thing he was trying to do was illegal. "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.'" This made Trump "really frustrated," he said.

The former secretary of state implied this is part of what led to the deterioration of his relationship with Trump, which ultimately resulted in his firing in March. "I think he grew tired of me being the guy every day that told him, 'You can't do that,'" he explained. It didn't help matters that according to Tillerson, the two also didn't "have a common value system."

Upon announcing his secretary of state's firing in March, Trump said that he "got along well with" with Tillerson, who had reportedly called him a "moron" during a Pentagon meeting. Watch Tillerson's comments below. Brendan Morrow