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The ear, nose, and throat doctor also reportedly took a selfie while Rivers was under anesthesia - a major violation of privacy.
But Korovin wasn't new to treating high profile stars. The 56-year-old counts Lady Gaga, Hugh Jackman, Ariana Grande, John Mayer, and Brooke Shields among her many celebrity clients.
Her Facebook page - which has since been cleared of all pictures and information - once showcased many photos of the doctor working and socializing with her A-list clients.
Now, Dr. Korovin's Facebook page is under attack by angry Joan Rivers fans:
But others, many in the medical community, are coming to Korovin's defense:
On September 4th, Joan Rivers died at the age of 81 after Korovin allegedly performed an unplanned biopsy without the comedian's permission.
After Dr. Lawrence Cohen, Rivers' gastroenterologist, discovered something on her vocal cords, Korovin, who wasn't authorized to perform any medical procedures at the Yorkville Endoscopy clinic, took over and began a biopsy. It was then that Rivers' vocal cords began to swell, cutting off her oxygen and leading to her death.
Dr. Cohen, who was also the clinic's medical director, has since parted ways with Yorkville.
The clinic confirmed his departure, stating, Dr. Cohen "is not currently performing procedures…nor is he currently serving as medical director."
Korovin's office said in a statement: "We do not comment on matters related to patients."
The Daily Mail snapped pics of Korovin arriving at her West Village home this weekend.
Korovin also appeared in Celine Dion's 2010 documentary "Through the Eyes of the World," in which she inspected the singer's strained vocal chords and joked around with her during a laryngoscopy procedure:
On Sept. 5, the New York Medical Examiner's Office told TheWrap that the autopsy on Rivers' body "did not determine the cause or manner of death, and that further studies would be conducted to determine exactly how she died."