Last week, President Trump said that he hadn’t realized how difficult it would be to disarm North Korea until he received a short history lesson from Chinese President Xi Jinping. “After listening for 10 minutes, I realized it’s not so easy,” Trump confessed to the Wall Street Journal.

But it appears Xi’s impromptu North Korea 101 class didn’t go quite far enough. Trump doesn’t seem to know exactly who the leader of North Korea is — or have any grasp of how long he’s been in power.

Speaking to Fox News about rising tensions with Pyongyang, Trump repeatedly referred to “the gentleman” leading North Korea as an individual who had persistently outwitted US administration after administration, at least as far back as the Clinton era of the 1990s.

“I hope things work out well. I hope there’s going to be peace, but they’ve been talking with this gentleman for a long time. You read Clinton’s book and he said, ‘Oh, we made such a great peace deal,’ and it was a joke,” Trump said in an interview on Fox & Friends that aired Tuesday. “You look at different things over the years with President Obama. Everybody has been outplayed. They’ve all been outplayed by this gentleman.”

.@POTUS on tensions between U.S. and North Korea pic.twitter.com/k10z2tUxbH — FOX & friends (@foxandfriends) April 18, 2017

As NBC News’s Bradd Jaffy pointed out, Trump seems to be implying that all these administrations have dealt with the same leader. But Kim Jong Un, North Korea’s current leader, only took power in 2011, during the Obama years. He took the reins after the death of his father, Kim Jong Il, earlier that same year.

The Clinton administration’s dealings with North Korea over nuclear weapons were with Kim Jong Il, and in fact the crucial precursor to the deal they struck over nuclear weapons was negotiated with his predecessor, Kim Il Sung, the current North Korean leader’s grandfather.

In other words, the wily “gentleman” that Trump is so concerned about is arguably three wily gentlemen.

It’s easy to laugh at the gaffe, but Trump’s ignorance about the leadership of one of the most dangerous nations on earth is deeply worrying given that tensions between the US and North Korea are increasing by the day. It’s hard to persuade a rogue leader to back down, after all, when you don’t exactly know who that rogue leader is.