We still don't know for sure what caused Joan Rivers' tragic death.
According to sources at the clinic, Dr. Lawrence Cohen, a world-renowned doctor who co-founded Yorkville Endoscopy, was asked to step down from the board there.
He also has apparently been on administrative leave since August 28th.
Sources report that the board took issue with Dr. Cohen allowing Joan's ear-nose-throat doctor to step in and perform or help with some kind of procedure, even though he wasn't licensed at the clinic.
It was reported that procedure was an unauthorized biopsy, but the clinic is denying that.
[Image via FayesVision/WENN.]