Former National Security Adviser Michael Flynn's lead attorney told "Hannity" Thursday she was "extremely disappointed and saddened" by U.S. District Judge Emmet Sullivan's order appointing a third party to argue against the Justice Department's motion to dismiss the case against the retired Army lieutenant general.

"I am personally extremely disappointed and saddened by his reaction," Sidney Powell told Sean Hannity.

"I don't know, I am mystified by the entire thing," she later added. "It's not like the Judge Sullivan I knew ... at all. I can’t explain it."

Sullivan's order appoints retired federal judge John Gleeson "to present arguments in opposition to the government's motion to dismiss" the matter -- and to consider whether the court should hold Flynn in contempt for perjury. The precise reasons for the perjury review were not clear in Sullivan's order.

"I am mystified by the entire thing. It's not like the Judge Sullivan I knew ... at all."

— Sidney Powell, 'Hannity'

Gleeson has openly criticized the Trump administration's handling of Flynn's case, raising concerns that he was selected to improperly bolster Sullivan's efforts to keep the Flynn case alive even though both the government and defendant want it dismissed.

DERSHOWITZ RIPS JUDGE'S LATEST MOVE IN FLYNN CASE

In a 2018 courtroom outburst, Sullivan suggested Flynn may have committed treason and has seemingly confused key details about Flynn's overseas lobbying work.

Last year, Flynn abruptly abandoned his plan to provide testimony against a former associate, after admitting that he had lied on federal forms required under the Foreign Agents Registration Act (FARA). Flynn has said he received constitutionally inadequate legal advice.

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"We have been the victims of astonishing Brady violations for three years now," said Powell, using a common term to describe breaches of the prosecutorial obligation to disclose exculpatory evidence to a defendant. "Some of the information we've just been given was in the possession of [the] special counsel [Robert Mueller], and of course was in the possession of the FBI before that.

"The FBI knows that its agents made up of the purported false statements and then that special counsel statements made up the purported filing," she went on. "The government was the only institution that lied in this case. General Flynn was honest with the agents and they reported that back."

Fox News' Gregg Re contributed to this report.