Before Stephen Colbert welcomed Fire and Fury author Michael Wolff as his guest Monday night, he decided to catch his audience up on just how insane the portrayal of President Donald Trump is in the bombshell new book.

“If you have not read it yet, here are the CliffsNotes,” the Late Show host told his audience. “Trump dumb, staff worried.”

“This book has led a lot of people to wonder whether Donald Trump is mentally stable enough to be president,” he added. “Spoiler alert: He’s not,” Colbert whispered into the camera as an expression of abject fear crossed his face.

Colbert also had a field day with Trump’s Twitter defense, in which he called himself “like, really smart” and a “very stable genius.”

“Being ‘like, really smart’ is not the same as being really smart, sir,” he told the president. “Also, I think it’s worth mentioning that people who are mentally stable don’t usually announce it. If you’re going under for surgery, the last thing you want to hear your doctor say is, ‘Don’t worry, I’m mentally stable and, like, really smart!’”

Imitating Trump, Colbert said, “Yes, I’m a very stable genius, now if you’ll excuse me, it’s past my cheeseburger’s bedtime.”