(CNN) Steve Bannon was interviewed by special counsel Robert Mueller's team last Friday, a person familiar with the matter said.

Friday's interview was at least the third time the estranged adviser to President Donald Trump has met with Mueller's team. The source said Bannon has never appeared before the Mueller grand jury.

The Washington Post first reported that Bannon had been interviewed Friday by the special counsel team. Its report, citing sources familiar with the session, said Bannon had been asked about comments that Roger Stone, a longtime associate of Trump, had made about WikiLeaks in 2016.

Bannon, a former White House chief strategist, left his role in the administration last year after joining Trump's campaign in a leading role through its final months. But he and the President had a falling-out in January of this year after Bannon was quoted calling an infamous 2016 meeting of a Russian lawyer, Donald Trump Jr., then-campaign chief Paul Manafort and Jared Kushner "treasonous."

Bannon also was quoted at the time saying the Mueller investigation was "all about money laundering."

In the face of Trump's criticism, Bannon declined to hit back and expressed some regret.

He appeared to clash with the special counsel investigation early this year before striking a deal to be interviewed by investigators rather than going before a grand jury. CNN reported in February that the special counsel team questioned Bannon for hours over the course of two days.

As a key aide to Trump through the general election and the bulk of the President's first year in office, Bannon is one of the highest-profile members of Trump's circle known to have spoken with Mueller's team.

Word of his Friday interview with the investigators came the same day the Wall Street Journal reported that Mueller's investigators had renewed their focus on another witness in the probe, Jason Sullivan, who worked as a social media adviser to Stone during the 2016 campaign.

CNN has previously reported that Mueller subpoenaed Sullivan, who testified before the grand jury in June. According to the Journal, Sullivan also received a subpoena to turn over communications.

Sullivan told the Journal that Mueller's team had recently followed up with his attorney to ask about comments Stone might have made about Julian Assange, the founder of WikiLeaks.

CNN has previously reported on at least one of the conference calls where Stone discussed Assange.