It is unclear if Donald Trump knew at the time he was being filmed for a porn video.

Donald Trump started the day on Friday talking about sex tapes. At end of day Trump was still facing talk of sex tapes - though not the same one.

The Republican presidential nominee tweeted at 3am about suggestive footage that reportedly exists of former Miss Universe Alicia Machado, drawing fire from Democrat Hillary Clinton. But by day's end, Trump faced reports that he had appeared briefly in a pornographic video in 2000.

In the 13-second clip posted on BuzzFeed's website, Trump is seen on a street in New York fully clothed surrounded by young women as he uncorks a bottle of champagne and pours it over the bunny-ear Playboy logo printed on the side of limousine.

It is unclear if Trump knew at the time he was being filmed for a porn video, which the website said featured "fully nude women posing in sexual positions, dancing naked, touching themselves while naked, touching each other sensually, rubbing honey on themselves, taking a bath, and dressing in costumes."

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"There's been a lot of talk about sex tapes today," Clinton spokesman Nick Merrill said. "And in a strange turn of events only one adult film has emerged today and its star is Donald Trump."

Trump's campaign didn't immediately return calls for comment.

Clinton cited Machado in Monday's debate, saying Trump called the Venezuelan "Miss Piggy" after she gained weight. "She has become a US citizen and you can bet she's going to vote," Clinton said of the 1996 pageant winner.

Since then, Trump has defended the way he treated Machado and has sought to discredit her.

"Did Crooked Hillary help disgusting (check out sex tape and past) Alicia M become a U.S. citizen so she could use her in the debate?" Trump said on Twitter early Friday morning.

The Republican Party includes a statement in its official party platform about porn: "Its harmful effects, especially on children, has become a public health crisis that is destroying the lives of millions. We encourage states to continue to fight this public menace and pledge our commitment to children's safety and well-being."