This 1998 frame from video provided by C-SPAN shows George Nader, president and editor of Middle East Insight. As an adviser to Abu Dhabi's crown prince, Sheikh Mohammed bin Zayed Al Nahyan, Nader worked throughout 2017 with Elliott Broidy, a fundraiser for President Donald Trump, in a secretive lobbying effort to alter U.S. policy in the Middle East.

George Nader, a key witness in former special counsel Robert Mueller's probe of Russian interference in the 2016 election, pleaded guilty Monday to charges of shipping an underage boy to the U.S. for sex and possessing child pornography.

Nader, 60, faces a mandatory minimum sentence of 10 years in prison and a possible maximum of 50 years behind bars, the U.S. Attorney's Office for the Eastern District said in a press release Monday. Judges usually issue sentences below the maximum.

Federal prosecutors agreed to recommend the mandatory minimum sentence — 10 years in prison — for Nader as part of his plea agreement in U.S. District Court in Eastern Virginia, a spokesman for federal prosecutors told CNBC.

An attorney for Nader did not immediately respond to CNBC's request for comment. Nader, who is currently being held without bail, is scheduled to be sentenced April 10.

Last week, prosecutors filed a charging document known as an information, accusing Nader of two criminal counts. An information is typically filed in advance of a defendant entering a guilty plea.

Nader was accused in the first count of possession of visual depictions of minors "engaging in sexually explicit conduct" in late 2012.

He was accused in the second count of transporting a 14-year-old boy from Europe to the U.S. in February 2000 "with the intent that the boy engage in prostitution, or in any sexual activity for which any person can be charged with a criminal offense, or attempted to do so."

The press release Monday said that Nader "met the boy in Prague, Czech Republic, and later brought him to his residence in Washington, D.C."

"Nader also admitted that, in September 2012, he possessed or accessed with intent to view video images of child sexual abuse while he was in New York."

Federal prosecutors agreed dismiss a much more recent indictment against Nader on similar charges that was returned in July 2019.

Nader, a citizen of Lebanon and a wealthy Middle East power broker, had acted as a middle-man between U.S. and Russia-connected figures after President Donald Trump's election. Nader helped arrange a January 2017 meeting in the Seychelles between Erik Prince and Kirill Dmitriev, the head of Russia's sovereign wealth fund, who reported directly to Russian President Vladimir Putin, according to Mueller's report on his investigation.

Prince, founder of the private security company originally known as Blackwater, is the brother of Education Secretary Betsy DeVos.

Nader had already been convicted for transporting child porn in the same court back in 1991, according to the U.S. Attorney's press release.

Nader faces additional charges in federal court in Washington, D.C., for allegedly funneling millions in illegal campaign contributions to support Hillary Clinton's 2016 presidential campaign. Those charges are unrelated to Nader's child sex charges in Virginia.

-- CNBC's Dan Mangan contributed to this report.