As the past 35 months have made painfully clear, Donald Trump is not a particularly smart man. At least, not in the traditional way that Americans used to expect of their president. “We just got back from the Middle East,” he told a room full of Israelis, upon arriving in Jerusalem from Saudi Arabia last May. That same month, he asked editors from The Economist if they had ever heard of the phrase “priming the pump,” which is basically like asking a bunch of auto mechanics if they’re familiar with “steering wheels.” After the Ninth Circuit rejected the administration’s request to resume its travel ban, he tweeted, to the appeals court, “SEE YOU IN COURT.” He called his national security adviser in the middle of the night to find out if he should want a strong dollar or a weak one. He can’t spell to save his life. He’s still struggling with the difference between a trade deficit and a surplus. So while it shouldn’t come as a huge shock that the president doesn’t know the difference between two very different but similarly named diseases, it’s still nevertheless terrifying to have it confirmed.

On Thursday night, MSNBC’s All In with Chris Hayes aired footage of a presentation by Microsoft founder Bill Gates, in which the billionaire philanthropist told audience members at a Bill and Melinda Gates Foundation event that on two separate occasions, he had to explain to Trump that H.I.V. and H.P.V. are, in fact, not the same thing. The former, human immunodeficiency virus, is a sexually transmitted infection that can lead to AIDS. The latter, human papillomavirus, is an S.T.D. that causes genital warts and, in some cases, cervical cancer. “Both times he wanted to know if there was a difference between H.I.V. and H.P.V., so I was able to explain that those are rarely confused with each other,” Gates told the crowd. Trump, incidentally, is alleged to have forgone prophylactics during sexual encounters with adult-film stars and Playboy models, and has called dodging S.T.D.s his “personal Vietnam.” Women’s vaginas, he told Howard Stern in 1997, are “potential landmines” and “there’s some real danger there.”)

Perhaps more concerning, Trump apparently had to be talked out of launching a commission to investigate whether vaccinations cause autism and other developmental disorders, a fringe conspiracy that has been debunked by the medical community. According to Gates, during both meetings, Trump asked “if vaccines weren’t a bad thing because he was considering a commission to look into ill effects of vaccines.” (Gates said he told him, “No, that’s a dead end. That would be a bad thing, don’t do that.”)

And, of course, no new report on Trump’s mental state would be complete without a creepy anecdote about Trump and someone’s daughter.

Gates also discussed a time when Trump met his daughter, Jennifer Gates, at a “horse-show thing” in Florida. Jennifer is an “accomplished equestrian,” according to Business Insider. About 20 minutes after talking to Jennifer at the event, Gates said, Trump reappeared in style, flying in on a helicopter to the same place he had just been.

“So clearly he had been driven away, but he wanted to make a grand entrance in a helicopter,” Gates said, mimicking the flight path of Trump’s helicopter with his hand, eliciting another round of laughs. Gates added that his daughter came up in conversation when the pair first talked.

“It was actually kind of scary how much he knew about my daughter’s appearance,” Gates said. “Melinda didn’t like that.”

Scary, indeed.