The former Secretary of State spoke of global challenges before expressing his concern about "the state of our American democracy", particularly a "growing crisis of ethics and integrity".
Tillerson did not mention his former boss by name during the 22-minute speech but it was hard not to read much of his address as a veiled and fiery critique of the man who unceremoniously fired him in March.
"If our leaders seek to hide the truth, or we as people become accepting of alternative realities that are no longer grounded in facts, then we as American citizens are on a pathway to relinquishing our freedom", he said in a commencement address at the Virginia Military Institute in Lexington, Va. Trump later clarified that "Rex and I have been talking about this a long time", and used the Iran nuclear deal as an example of how "we were not really thinking the same".
Despite repeated denials from the White House that Trump and Tillerson were at odds, the president eventually replaced Tillerson with then-CIA director Mike Pompeo for the top USA diplomat position. "When we talk to our adversaries", he said, "we must say what we mean and mean what we say".
It wasn't only Trump who doubted Tillerson's performance in his former role, however.
"The President speaks for himself", Tillerson remarked at the time.
"Tillerson had zero respect for the State Dept press corps and only discovered their existence when he was an endangered species", wrote Axios' Jonathan Swan.
Rex Tillerson may be gone, but he hasn't forgotten.
Tillerson, who was sacked by Trump in March after little more than a year on the job, did not mention the U.S. president by name during his address to cadets at the school in Lexington, Virginia. "He basically says [in an interview for Farrow's new book] 'I didn't know what I was doing, I wasn't experienced enough for it'".
Still, Tillerson warned that obscuring the truth would lead America to become like "Russia, China, Iran or North Korea".
"A responsibility of every American citizen to each other is to preserve and protect our freedom by recognizing what truth is and is not, what a fact is and is not, and begin by holding ourselves accountable to truthfulness", Tillerson told the assembly.