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."