Washington (CNN) President Donald Trump's first national security adviser, Michael Flynn, has fired his lawyers who arranged a 2017 plea deal that helped set the tone for others to cooperate with special counsel Robert Mueller's investigation.

Flynn's attorneys, Rob Kelner and Steve Anthony, said in a court filing Thursday morning their longtime client was "terminating" them, and that he has already found new legal representation.

The new lawyer or lawyers have not yet announced who they are to the court.

The announcement also comes shortly after a transcript was released of a voicemail Kelner had received from Trump personal attorney John Dowd on the eve of Flynn's plea deal, suggesting the White House should be kept apprised of what Flynn was doing. Flynn turned that voicemail over to prosecutors -- and Mueller credited him for doing so. The voice mail became part of Mueller's investigation into whether Trump had tried to sway cooperators.

Flynn, who continues to delay his sentencing after a disastrous court hearing last December and subsequent developments that put the spotlight on the Covington & Burling law firm, was one of the Mueller's investigations earliest and important cooperators.

Read More