Fired White House chief strategist and ex-Trump campaign manager Steve Bannon has been subpoenaed by special counsel Robert Mueller, Fox News has confirmed.

The onetime Breitbart News executive chairman also testified behind closed doors on Capitol Hill Tuesday — for nearly 12 hours. Bannon appeared before the House Intelligence Committee as part of its Russia probe.

First reported by The New York Times, the Bannon subpoena was issued by Mueller’s team last week. Sources told Fox News that Bannon’s subpoena, which could require him to appear before a grand jury investigating Russian meddling in the 2016 presidential election, was issued after the FBI initially was unable to contact him.

“Even if you thought that was not treasonous, or unpatriotic, or bad s**t, and I happen to think it’s all of that, you should have called the FBI immediately." — Quote attributed to Steve Bannon in "Fire and Fury"

Sources familiar with the matter told Fox News that despite the subpoena to testify before a grand jury, there is a possibility that Bannon will, instead, be interviewed by Mueller’s office.

A spokesperson for Mueller did not immediately respond to Fox News’ request for comment.

Bannon left Capitol Hill on Tuesday after a nearly 12-hour, closed-door interview with the House Intelligence Committee where a top Democrat accused the president of placing a “gag order” on Bannon.

Rep. Adam Schiff, D-Calif., said Bannon refused to answer questions about his time in the White House or his work on the presidential transition. His refusal prompted a subpoena from the committee’s Republican chairman, Rep. Devin Nunes of California.

Schiff says that was the first time Republicans on the committee had issued a subpoena in response to a witness refusing to answer questions at the instruction of the White House. Schiff says that the committee plans to bring Bannon back for another round of questioning.

Rep. Trey Gowdy, R-S.C., confirmed Bannon’s refusal to talk on Fox News’ “Tucker Carlson Tonight.”

Gowdy told Tucker Carlson, “The reason we had a little hiccup this morning was because executive privilege now covers things before you become the chief executive, which is just mind-numbing, and there is no legal support for it. But, we can’t make a witness answer a question.”

Fox News has confirmed that Bannon will return to speak with the House Intel Committee Thursday afternoon.

Bannon’s subpoena and interview with congressional investigators came after the publication of Michael Wolff’s book, “Fire and Fury: Inside the Trump White House,” where Bannon made comments blasting Trump’s eldest son Donald Trump Jr., son-in-law Jared Kushner, and ex-campaign chairman Paul Manafort.

Bannon described their infamous June 2016 meeting in Trump Tower with Russian attorney Natalia Veselnitskaya during the campaign as “treasonous” and “unpatriotic.”

STEVE BANNON TESTIFIES BEFORE HOUSE INTEL COMMITTEE AS PART OF RUSSIA PROBE

“Even if you thought that was not treasonous, or unpatriotic, or bad s---, and I happen to think it’s all of that, you should have called the FBI immediately,” Bannon said in the book.

Bannon also said that Trump Jr. would be cracked “like an egg on live TV” in any possible public testimony about the situation.

The president issued a multi-paragraph, blistering takedown of Bannon, who left his White House post in August, suggesting that “sloppy Steve” Bannon had “lost his mind,” seeking to distance himself from his former chief strategist.

“Steve Bannon has nothing to do with me or my presidency,” Trump said in the statement. “When he was fired, he not only lost his job, he lost his mind.”

Bannon is just the latest Trump campaign associate to be summoned to interview with Mueller.

In October 2017, Manafort and his associate Rick Gates were indicted by a federal grand jury on 12 counts, as part of Mueller’s investigation. Both pleaded not guilty.

PAUL MANAFORT, RICK GATES INDICTED BY FEDERAL GRAND JURY IN RUSSIA PROBE

The special counsel’s office told Fox News that the counts included conspiracy against the United States, conspiracy to launder money, unregistered agent of a foreign principal, false and misleading Foreign Agent Registration (FARA) statements, false statements and seven counts of failure to file reports of foreign banks and financial accounts.

Fox News learned Tuesday that Manafort’s next court appearance would be Feb. 14 for a status hearing. The government had proposed the trial begin May 14, but the date may be pushed to October. At this point, there is no official start date.

FORMER TRUMP AIDE GEORGE PAPADOPOULOS PLEADS GUILTY TO MAKING FALSE STATEMENTS TO THE FBI

Mueller’s team also charged former Trump campaign foreign policy adviser George Papadopoulos with making false statements to FBI agents about his contacts with people close to the Russian government. Papadopoulos pleaded guilty to the charges in the Mueller investigation.

Fox News’ Jake Gibson, Paulina Dedaj, Chad Pergram and The Associated Press contributed to this report.