The FBI agent who was removed from Special Counsel Robert Mueller’s investigation into possible ties between the Trump campaign and Russia — because he sent anti-Trump messages to a colleague — oversaw the bureau’s interviews with ousted National Security Advisor Michael Flynn, Fox News confirmed on Monday.

Peter Strzok, a former deputy to the assistant director for counterintelligence at the FBI, also was confirmed to have changed former FBI Director James Comey’s early draft language about Hillary Clinton’s actions regarding her private email server from “grossly negligent” to “extremely careless.”

The language being edited was important because classified material that’s been mishandled for “gross negligence” calls for criminal consequences, analysts point out.

MUELLER AIDE FIRED FOR ANTI-TRUMP TEXTS NOW FACING REVIEW FOR ROLE IN CLINTON EMAIL PROBE

Flynn pleaded guilty Friday to lying to the FBI about reaching out to Russian officials. Prosecutors said Flynn in December 2016 asked Russia's ambassador to the U.S., Sergei Kislyak, not to escalate the situation after the outgoing Obama administration imposed sanctions on Russia in retaliation for suspected election interference.

Flynn left the White House in February after acknowledging that he had given an incomplete account to Vice President Mike Pence about his contacts regarding Russia.

The wording change came to light last month after newly reported memos to Congress showed that a May 2016 draft of Comey’s statement closing out the email investigation accused the former secretary of state of being “grossly negligent.” A June 2016 draft stated Clinton had been “extremely careless.”

The modified language was final when Comey announced in July 2016 that Clinton wouldn’t face any charges in the email investigation.

Strzok is being reviewed by the Justice Department’s Office of Inspector General for the role he played in the Clinton email investigation.

A source close to the matter told Fox News that the probe, which will examine Strzok's roles in a number of other politically sensitive cases, should be completed by "very early next year."

Fox News' Jake Gibson, James Rosen and The Associated Press contributed to this report.