Asked about Tillerson's IQ later Tuesday, a State Department spokeswoman responded that he had a "high" IQ.
Tensions between Trump and Tillerson appeared to escalate last week when NBC News reported that Tillerson considered resigning this summer. It said Tillerson also called the president a "moron" following a July meeting with members of the president's national security team and Cabinet.
At a hastily scheduled news conference after the report, Tillerson said he never considered leaving his job but did not deny calling the president the derogatory name.
NBC later reported that Tillerson's refusal to deny calling Trump a moron angered the president further.
NBC, which shares a parent company with CNBC, stands by its reporting.
Read the full Forbes story here.
Disclosure: NBC and CNBC are owned by NBCUniversal, a division of Comcast.