Amid reporting that White House chief of staff John Kelly may resign in the days to come, CNN is also reporting that Kelly was questioned by special counsel Robert Mueller’s team in recent months.

The report, based on three sources, said the questions narrowly focused on President Trump’s possible obstruction issues that Mueller is said to be investigating. Kelly’s interview is noteworthy in that he joined the White House relatively late — in July 2017 — compared to other prominent witnesses in Mueller’s probe who were in Trump’s inner circle during the campaign, the transition, or the early days of the administration.

The special counsel’s team questioned Kelly specifically on an episode involving Trump after the New York Times reported that last year Trump sought to fire Mueller — a report that allegedly drew Trump’s ire at then-White House counsel Don McGahn, who didn’t publicly deny it.

The White House at first resisted Mueller’s request to question Kelly, CNN reported, a departure from an initial posture geared toward cooperation with Mueller. The request came, a source told CNN, after the FBI raids on Michael Cohen, when anxiety about Mueller was particularly high in the White House.

Read the report here.