A key witness from the Robert Mueller investigation got slapped with sex trafficking charges on Friday.

Businessman George Nader, 60, was already facing child pornography charges — and he has a long history of sexually abusing minors.

His latest indictment came down in federal court Friday and was in connection to an alleged trip that Nader took with a 14-year-old boy to Europe, where he is accused of engaging in sex acts with him.

Authorities had been probing the Lebanese-American — who was said to be a liaison between the Russians and President Trump’s transition team — since last year after allegedly discovering child porn and images of bestiality on his phone. He was arrested in June at JFK Airport and initially charged with “transporting visual depictions of minors engaged in sexually explicit content,” according to DOJ officials.

Nader pleaded guilty in the Eastern District of Virginia to the exact same charges in 1991.

The convicted child rapist was also found guilty of sexually abusing at least 10 minors in the Czech Republic back in 2003, but he was only sentenced to a year in prison.

Nader’s name appears more than 100 times in the redacted version of special counsel Mueller’s report. He allegedly served as an adviser to the United Arab Emirates in April 2017 and was said to have funneled money to a top Trump fundraiser using a company in Canada.

Authorities plan to keep Nader jailed until he stands trial. His first court date is Sept. 30.

With Post wires