President Trump suggests a way to settle Rex Tillerson's reported "moron" comment: an IQ test.
"I think it's fake news, but if he did that, I guess we'll have to compare IQ tests. And I can tell you who is going to win," Trump told Forbes of the "moron" comment.
Trump often boasts about his intelligence and achievements.
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.
Disclosure: NBC and CNBC are owned by NBCUniversal, a division of Comcast.