United States President Donald Trump on Friday called former Secretary of State Rex Tillerson “dumb as a rock” after Tillerson said the president had pushed him to take illegal actions, reported The New York Times.

“Mike Pompeo [secretary of state] is doing a great job, I am very proud of him,” Trump said. “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!”

Trump had sacked Tillerson in March after a series of rifts over policy on North Korea, Iran and Russia. The relationship between the president and the former Exxon chief became strained after Tillerson reportedly called Trump a moron at a July 20, 2017, meeting at the Pentagon where other Cabinet members were present.

In an interview with CBS on Friday, Tillerson described the president as “undisciplined”. “It’s challenging for me coming from the disciplined, highly process-oriented ExxonMobil Corporation… 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 said.

Tillerson had also said that Trump pressed for actions beyond his authority. Tillerson said: “When the president would say, ‘Here’s what I want to do and here’s how I want to do it,’ 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.”

When Trump had appointed Tillerson, he had had much praise for him. Trump had called him an “excellent choice for secretary of state” because of his “tenacity, broad experience and deep understanding of geopolitics”, The Guardian reported.

The spat comes even as Trump’s current Chief of Staff John Kelly is expected to resign soon after differences with the president.