EXCLUSIVE: Revealed, The 'Throat Specialist To The Stars' Who Was Not Authorized To Be In The Room With Joan Rivers Before The Star Went Into Cardiac Arrest

• Dr Gwen Korovin counts Hugh Jackman, Julie Andrews, Ariana Grande and Lady Gaga as patients
• It is believed she watched Dr Lawrence Cohen, of Yorkville Endoscopy clinic, carry out a throat procedure on Joan Rivers on August 28
• Comedienne Joan, 81, then suffered a cardiac arrest when a biopsy was performed on her vocal cords, sources reveal
• CNN reports a staff member at Yorkville told investigators Joan's personal doctor even took a 'selfie' photo in the procedure room while star was under anesthesia
• Joan died on September 4 at Mount Sinai Hospital in New York
• Her daughter Melissa is still 'too raw' to think about launching legal action against clinic and her mother's doctors, sources tell MailOnline
• The New York State Department of Health is 'still investigating'

A doctor known as the throat specialist to the stars was in attendance during the procedure that led to Joan Rivers’ death.

Dr Gwen Korovin, 56, who counts Hugh Jackman, Julie Andrews, Lady Gaga, pop princess Ariana Grande and Celine Dion among her celebrity patients, is an esteemed ear, nose and throat specialist based in Manhattan.

It is believed that Dr Korovin was at Yorkville Endoscopy clinic on August 28 as Joan’s personal doctor when the legendary comedienne stopped breathing while undergoing a procedure on her vocal cords.

Today, a member of staff at Dr Korovin’s offices on East 77th Street said: ‘We’re not commenting at this time due to the professional duty we have to our patients.’

Pictured at the weekend, Dr Korovin arrived back at her Manhattan home after calling ahead to inquire whether any media was waiting for her, sources said.

CNN reports that a source close to the investigation into Joan's death being carried out by the New York State Department of Health said the star suffered a cardiac arrest as her personal doctor performed a biopsy on her vocal cords.

A staff member at Yorkville Endoscopy clinic told investigators that the doctor even took a 'selfie' photo in the procedure room while Joan was under anesthesia, the source said.

Joan, 81, arrived at the Upper East side clinic for an endoscopy with gastroenterologist Dr. Lawrence Cohen, Yorkville's medical director, on the morning on August 28.

The procedure was intended to help diagnose her hoarse voice and sore throat, and involved the insertion of a camera down her throat.

An ear, nose and throat specialist - who was not certified by the clinic, as required by law - then performed a biopsy on the star's vocal cords.

The doctor was described by the source as Joan's personal ENT specialist.

CNN said that investigators believe that Joan's vocal chords began to swell during the biopsy, cutting off the flow of oxygen to her lungs, which led to cardiac arrest.

The comedienne was rushed to nearby Mount Sinai hospital from the clinic.

However, she never regained consciousness and died on September 4 after being taken off life support and spending her final days with her daughter Melissa Rivers by her side and her loved ones paying their final respects.

On Friday, Dr Cohen stepped down from his position at the medical center.

A Yorkville spokesperson confirmed to MailOnline: 'Dr Cohen is not currently performing procedures at Yorkville Endoscopy; nor is he currently serving as medical director.’

Sources told ABC news that Dr Cohen had allowed a specialist, who was not authorized to practice at the clinic, to examine Joan.

Neither Dr Cohen nor the specialist have been accused of wrongdoing.

Today, the New York State Department of Health, in a statement to People, said:

'The State Department of Health's investigation is ongoing. As this is an open investigation, DOH cannot comment on any specifics regarding the investigation.'

The New York Times said that Joan went to a clinic for the procedure rather than a hospital to avoid publicity.

One member of staff at the clinic actually assumed that Joan's personal doctor was actually her make-up artist, The Times said, adding: ‘When the E.N.T. arrived, she was identified as an observer, not a doctor. She carried a bag, according to one of the people briefed, and the clinic staff members who saw her entering the operating room assumed that she was a makeup artist there to help make Ms. Rivers look her best after the operation.’

In a Wag magazine article published last year, Dr Korovin told how she rushes to see her celebrity clients with her bag in hand, saying: ‘The black bag I bring to their dressing rooms has everything I need to administer on-the-spot treatment.

If needed, I will see them later in my office.'

Pictures posted on her Facebook page show Dr Korovin posing by pictures of her famous patients including Harry Potter star Daniel Radcliffe in her Upper East side office.

While not yet making any comment on the death of Joan Rivers, Dr Korovin has only ever been acclaimed by her famous patients.

She has told how she does not like to resort to any rash action, saying: ‘ Patients come to me with a range of complaints and I treat them all, including performing surgery when needed – like the removal of polyps and cysts – and treating upper respiratory problems and cleaning out sinuses.

'I like to be conservative and go as far as possible with medical treatment before doing surgery.'

Stage star Nathan Lane credits her with helping him through previews of “The Nance” last year.

“I was fighting a bronchial infection. I don’t think I would have made it through opening night without her.”

Dr Korovin also counts Hugh Jackman as one of her high-profile patients.

The Australian star brought down the house as he performed Quiet Please, There’s a Lady on Stage, from the musical, The Boy From Oz, at Joan’s funeral in New York.

In a 2013 interview with the Daily News, Dr Korovin was hailed as ‘Broadway’s throat doc’ and the ‘keeper of high profile pipes’.

Indeed, in 1998 Celine Dion even thanked the specialist when she won a Grammy.

The profile says:‘The walls in the ear, nose and throat doctor’s upper East Side office are lined with pictures and thank-you notes from stars who’ve opened wide and said ahh: Hugh Jackman, Kristin Chenoweth, Julie Andrews, Barbara Cook and Brooke Shields, to name a few.’

She also helped singer John Mayer through his recent vocal-cord issue.

'We’re friendly,' said Dr Korovin when asked if Mayer was up to his flirty ways in her office.

'There’s a mutual respect. You get to know your patients very well.'

That includes Lady Gaga, whose mother referred her to Dr Korovin. And despite Gaga’s eccentric behaviour and get-up, her vocal cords ‘are just like everyone else's', says the doctor.

Despite this, the profile added that not all of Dr Korovin’s patients are stars and Broadway legends, saying 'She treats upper East Side society types and more average New Yorkers.'

In Wag magazine, Dr Kerovin told how she often interrupts weekends at her country home in Westchester to help high-profile performers between matinee and evening performances.

She is also pictured treating pop sensation Ariana Grande with a vitamin B12 shot before an appearance with Jimmy Fallon - a photo which Ariana posted to her Instagram account..

'I treat patients backstage many times a year,' she said.

Meanwhile, a source told MailOnline that Melissa is still 'very raw' and has not yet thought about launching legal action against Yorkville or Joan's personal doctor, saying: 'I was told that the family was not going to do anything, but that was a few days ago, so who knows what will happen.'

Neither Dr Korovin or her attorney husband Jack Uram returned telephone messages