(Washington Post) - What is known about comedian Stephen Colbert's surprise trip to Russia? He was there last week. He appeared on a Russian talk show and "announced" that he was considering a run for president of the United States in 2020. And, as you may expect, it gave him even more opportunities to mock President Donald Trump.

Amid allegations that Mr Trump's campaign colluded with Russia in the 2016 presidential election, the Late Show host took his crew overseas to film in St. Petersburg. Colbert didn't spill many details on Monday night's show, except to say that the footage will be used in an upcoming week of shows all about his trip, which he called "fascinating". Colbert, who arrived back in the US on Sunday night, said the excursion took many months of planning; he and his crew shot 13-hour days and filmed about four or five segments.

"The Russian people were lovely," he said, adding that they visited "the most incredible locations".

Naturally, he also got in a few digs about Mr Trump and the Russia investigation. "You know who did know I was in Russia? Russian intelligence," Colbert said. "Hardcore fans, evidently, followed me everywhere."

"Also got some attention from American intelligence," he added. "It's important to keep your eye on a comedian while he's in Russia doing jokes. I could be over there, I could be giving state secrets to the Russians. Oh, wait - someone's already got that covered."

He showed a clip of his guest appearance on the Russian late-night show Evening Urgant last Friday, where he sat on the other side of the desk for once, bantering with host Ivan Urgant through a translator and playing "Russian roulette" with a tray of vodka-filled shot glasses and pickles.

Midway through their game, the American comedian interrupted the host to say he had something to disclose - but only if he could confirm first that the show wasn't broadcast in the US. "I am here to announce that I am considering a run for president in 2020," Colbert said, delivering what was ostensibly a joke with a straight face. The audience applauded as he nodded seriously. "And I thought it would be better to cut out the middleman and just tell the Russians myself," he continued. "If anyone would like to work on my campaign in an unofficial capacity, please just let me know."

The "announcement" was an obvious jab at President Trump. Stateside, Colbert has been one of the most vocal critics of Mr Trump, making the president the chief target of CBS's late-night show.

Colbert said on Monday: "Now to be clear, all I said in that little clip there was that I was considering a run. If I decide to run, obviously I'm not going to ask the Russians to help my campaign, OK? I would have my son-in-law ask them."

He added: "Like President Trump, I can neither confirm nor deny the existence of any other tapes of what I did in Russia. I did not personally make any such recordings. But I'm pretty sure my crew did."

As a bonus, Colbert threw in some mockery about late-night TV. "For those of you not familiar with late-night TV in Russia, it might seem a little foreign. Let me explain it to you. A white male host does some monologue jokes, then sits behind a desk to interview celebrities. It works over there somehow, I'm not sure."