BETHESDA, Md. (NewsNation Now) — President Donald Trump briefly left the military hospital where he is being treated for COVID-19, riding in a Secret Service vehicle to greet supporters gathered outside.

Trump departed the hospital in an armored SUV and remained in the vehicle as he drove past a flag-waving and cheering crowd outside Walter Reed National Military Medical Center.

Trump teased his surprise departure in a brief video posted to his Twitter page.

“I also think we’re going to pay a little surprise to some of the great patriots that we have out on the street,” he said, after thanking the doctors at the facility.

Trump did not alert the pool of reporters who are supposed to travel with him before leaving the hospital.

Trump said in the video that he had “learned a lot” about the virus getting it himself.

“I learned it by really going to school,” he said. “This is the real school, this isn’t the ‘let’s read the books’ school. And I get it and I understand it. And it’s a very interesting thing.”