Flynn prepared to testify that Trump directed him to contact Russians about ISIS, confidant says Flynn has pleaded guilty to one count of lying to the FBI.

 -- Retired Lt. Gen Michael Flynn has promised “full cooperation” in the special counsel’s Russia investigation and, according to a confidant, is prepared to testify that Donald Trump directed him to make contact with the Russians, initially as a way to work together to fight ISIS in Syria.

The stunning turn comes as Flynn pleaded guilty to one count of lying to the FBI about his back-channel negotiations with the Russian ambassador – talks that occurred before Trump took office. The special counsel made the plea agreement public Friday morning.

The confidant provided ABC News with new details on Friday about Trump’s instructions to Flynn. During the campaign, Trump asked Flynn to be one of a small group of close advisors charged with improving relations in Russia and other hot spots. The source said Trump phoned Flynn shortly after the election to explicitly ask him to “serve as point person on Russia,” and to reach out personally to Russian officials to develop strategies to jointly combat ISIS.

The confidant told ABC News that Flynn felt abandoned by Trump in recent weeks, and told friends about the decision to make the plea deal within the last 24 hours as he grew increasingly concerned about crippling legal costs he would face if he continued to contest the charges.

“Flynn is very angry,” the confidant told ABC News Friday. “He will cooperate truthfully on any question they ask him.”

In a prepared statement, Flynn expressed regret, but also stood defiant against the more scurrilous allegations that circulated about his work with Russia.

“It has been extraordinarily painful to endure 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.”

Richard Frankel, a former senior aide to Flynn and an ABC News contributor, said Flynn made his decision to cooperate under immense pressure, but he believes it is the right move for the country.

“I don't know how much General Flynn knows about any criminal activity that took place during the campaign or in the White House,” said Frankel, who also served in a senior role at the FBI. “However, General Flynn was a top adviser to President Trump in the campaign and a top adviser to him when he entered into the WH so if there are bodies buried so to speak, General Flynn would know about them in my opinion.”

Flynn was charged with lying to the FBI about the nature of his conversations with then-Russian ambassador to the United States Sergey Kislyak during the presidential transition. Those conversations led Russian officials to temper their response to increased U.S. sanctions, according to the charging documents.

The charge carries a penalty of up to five years in prison, but according to court documents, Flynn likely faces a sentence of zero to six months.

The White House had claimed it was unaware of the substance of those conversations, but today’s court documents show Flynn was acting specifically at the direction of senior transition team officials.

On the same day President Obama imposed tough sanctions on Russian facilities in the U.S. for meddling in the election, the Russian ambassador called Flynn to talk about them. After that conversation, Flynn consulted with a senior transition team official who said the Trump “did not want Russia to escalate the situation,” so Flynn relayed the request directly to Kislyak.

Russian officials tempered their response to increased U.S. sanctions, and President-elect Trump then tweeted: “Great move on delay (by V.Putin)—I always knew he was very smart!”

The documents also show that “a very senior member” of the transition team, which ABC News has learned was Trump’s son-in-law Jared Kushner, told Flynn to contact Russia about a United Nations resolution involving Israel.

The President has denied directing Flynn to make the contacts.

“No, I didn’t direct him,” Trump said in February, “but I would have directed him if he didn’t do it, okay?”

Flynn became the latest and most-senior Trump associate to face charges in Mueller's probe and arrived at the U.S. District courthouse accompanied by his wife and attorney Robert Kelner after having been processed at the FBI Washington Field Office, where he was fingerprinted and photographed, according to FBI officials.

In court, the retired lieutenant general was asked by Federal Judge Rudolph Contreras if he had ever been a part of similar proceedings, to which Flynn replied that he had not. Contreras then asked Kelner whether he was correct in assuming that Flynn was pleading guilty.

"Yes, your honor," said Kelner.

After the hearing, Flynn was free to go, but has to check in with authorities each week. Sentencing has been put off for now — and the judge noted that Flynn is agreeing to cooperate with authorities in other matters.

Flynn had initially resisted cooperating with the investigation, according to people close to the retired general, but he has been facing mounting legal debts and plans to sell his house to help defray costs.

He only recently learned the full scope of the charges he could potentially face. Last week, Trump lawyers received calls from Kelner, alerting them that he could no longer participate in information exchanges with other possible Mueller targets, the first public indication that a plea deal was in the works.

“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 of our country,” Flynn said. “I accept full responsibility for my actions.”

Trump and his legal team have learned of Flynn's decision via news reports Friday morning, according to sources with knowledge of the situation.

On Monday, Kelner was spotted exiting a meeting at Mueller’s offices in Washington, ABC News reported.

Flynn is a decorated military officer who once headed the Defense Intelligence Agency and, after leaving government, spoke frequently at Trump campaign rallies. He began facing scrutiny after it was learned he took payment to attend a Russian television event, at which he appeared seated next to Russian President Vladimir Putin.

That scrutiny only increased after he took over as Trump’s national security adviser. He was ultimately forced to resign after just a few weeks on the job after it was revealed that he misled Vice President Mike Pence and other administration officials about his meeting with the Russian ambassador.

Flynn initially denied that he discussed U.S. sanctions placed on Russia with Kislyak, but transcripts of Flynn and Kislyak’s phone calls reviewed by Justice Department lawyers showed otherwise.

Flynn was paid over $500,000 by foreign clients for consulting work and speaking fees – including contracts he allegedly failed to list on applications for security clearances and financial disclosure forms. He also only belatedly disclosed lobbying work his firm engaged in on behalf of the Turkish government.

Trump reportedly attempted to persuade the FBI to drop its investigation into Flynn’s conduct. In a Feb. 14 meeting at the White House, Trump reportedly told then-FBI Director James Comey to “let this go.”

“I hope you can see your way clear to letting this go, to letting Flynn go,” Trump told Comey, according to a memo Comey wrote afterwards, which was later described by the New York Times. “He is a good guy. I hope you can let this go.”

On Oct. 30, two members of Trump's campaign staff, former campaign chair Paul Manafort and his longtime associate Rick Gates, were indicted on 12 counts brought by Mueller's team related to work done prior to joining the Trump campaign, including conspiracy against the U.S., conspiracy to launder money and serving as an unregistered agent of a foreign principal.

That same day, it was also revealed that a third Trump campaign adviser, George Papadopoulos, pleaded guilty earlier in the month to making false statements to FBI agents probing his attempts to arrange a meeting between Russian officials and the campaign.

Correction: During a live Special Report, ABC News reported that a confidant of Lt. Gen. Michael Flynn said Flynn was prepared to testify that then-candidate Donald Trump instructed him to contact Russian officials during the campaign. That source later clarified that during the campaign, Trump assigned Flynn and a small circle of other senior advisers to find ways to repair relations with Russia and other hot spots. It was shortly after the election, that President-elect Trump directed Flynn to contact Russian officials on topics that included working jointly against ISIS.

ABC News' Adam Kelsey, Veronica Stacqualursi, Jack Date, Geneva Sands, Mike Levine, Trish Turner and John Santucci contributed to this report.

Criminal Information

Plea Agreement

Statement of the Offense