Former national security adviser Michael Flynn is reportedly planning to testify against President Trump and members of his family and intends to say then-president-elect Trump told him to make contact with Russians, according to a report.

ABC News reported that Flynn, who was charged with one count of lying to the FBI about his contacts with the Russian ambassador, promised to cooperate fully with special counsel Robert Mueller, who is overseeing the probe into Russian meddling in the 2016 election.

Flynn, who served as Trump’s national security adviser, also intends to testify against the president, members of his family, and others working in the White House, a source close to Flynn told ABC News.

Flynn appeared in court Friday and, as part of his plea deal, said a top member of the Trump transition team instructed him in December 2016 to reach out to Russian officials, according to the Associated Press.

The former national security adviser is reportedly “distraught” about his decision to cooperate with Mueller, a decision he made within the last 24 hours, but feels he is acting in the best interest of the country. Flynn is facing legal bills topping $1 million stemming from the investigation, according to ABC News.

"After over 33 years of military service to our country, including nearly five years in combat away from my family, and then my decision to continue to serve the United States, it has been extraordinarily painful to ensure these many months of false accusations of 'treason' and other outrageous acts," Flynn said in a statement. "Such false accusations are contrary to everything I have ever done and stood for. But I recognize that the actions I acknowledged in court today were wrong, and through my faith in God, I am working to set things right.

"My guilty plea and agreement to cooperate with the Special Counsel's Office reflect a decision I made in the best interests of my family and our country. I accept full responsibility for my actions."

Mueller’s office announced Friday morning that Flynn is charged with one count “willfully and knowingly” making “false, fictitious and fraudulent statements” to the FBI. Flynn made the false statements while he was working in the White House, which is what got him fired from the Trump administration.

He appeared in federal court Friday morning and pleaded guilty.

Editor's note: This story has been updated to reflect ABC News' acknowledgment that when Michael Flynn reportedly plans to testify that President Trump told him to make contact with the Russians, he will say it happened when Trump was president-elect, not a candidate.