What do a couple billionaires talk about when they meet? In the case of President Trump and Microsoft founder Bill Gates, it turns out they talk about sexually transmitted diseases.

In a video obtained by MSNBC, Gates revealed that on two occasions he met with Trump after the election, once at Trump Tower in December 2016 and then in March 2017 at the White House, Trump asked him if human immune deficiency virus and human papillomavirus were the same thing.  

"Both times he wanted to know if there was a difference between HIV and HPV. So, I was able to explain that those are rarely confused with each other," Gates told the audience that began to roll with laughter. 

Gates was speaking during a meeting of the Bill and Melinda Gates Foundation staff earlier this week, according to MSNBC host Chris Hayes. 

Gates also described a time he saw Trump speaking with his 22-year-old daughter, Jennifer Gates. 

"And then, like 20 minutes later, he flew in in a helicopter to the same place. So, clearly he had been driven away, but he wanted to make a grand entrance in a helicopter," Gates said. 

"When I first talked to him, it was actually kind of scary how much he knew about my daughter's appearance," Gates said. "Melinda didn't like that too well." 

Gates said when he met with Trump the newly elected president asked him if vaccines were a "bad thing" and that Trump told him he was exploring forming a commission to look into "ill effects of vaccines." 

"I said, 'No, that's a dead end. That would be a bad thing. Don't do that," Gates said. 

According to the Centers for Disease Control and Prevention, HIV is an entirely different virus from HPV. It is the most common STD, infecting 79 million Americans. In most cases, people with HPV do not have health problems, but it can cause genital warts and cancer.