Amy Blumenthal, pictured, started a romantic relationship with her psychiatrist after the doctor gave her an ultimatum, her family says. View Full Caption Legacy.com/Amy Michelle Blumenthal

FLATIRON — An Ivy League-educated psychiatrist pushed a deep-pocketed patient into a sexual relationship with her, quickly moved into her new lover's $5 million apartment overlooking Madison Square Park and became the main beneficiary of her squeeze's will, new court documents charge.

Dr. Susan Turner, 51, is accused of casting medical ethics aside by delivering an ultimatum to her patient of six months — end their professional relationship or date her.

The patient, lawyer Amy Blumenthal, opted for a romance with her shrink, even though she was on a witches' brew of psychotropic meds and had been going to Turner for therapy sessions three to five times a week, according to the court documents.

The two remained a couple for three and half years until Blumenthal died suddenly at 47 in August 2014. Blumenthal's death has since led to a bruising legal battle between Turner and her late lover's brother.

Randy Blumenthal claims in an affidavit filed earlier this month in Manhattan Surrogate's Court that Turner capitalized on his sister's weakened mental state and got Amy to change her will so Turner inherited her luxury pad in the Flatiron District and a trust holding $2 million.

"It is unethical for a psychiatrist to have a sexual relationship with a current or former patient because of the inherent balance of power which will always exist between the patient and doctor," Randy said in court papers asking a judge to invalidate the amendments to his sister's will that left Turner the bulk of her fortune.

"Dr. Turner abused this relationship and exerted her influence over Amy to change her estate plan," he said.

Turner has denied Randy's accusations, but has admitted she and Amy were an item. However, she says Amy was no longer her patient when they started dating.

She claims Randy, a hedge fund honcho who lives in Chelsea, never had a problem with the romance until Amy died and he learned that he wasn't getting any of her money.

"Simply put, [Randy] never expressed any dissatisfaction with Amy's and my romantic relationship during the approximately 3.5 years that we were together," she said in an affidavit.

"Now, [Randy] has made no secret of the fact that he fully intends to commence numerous litigations against me in what can only be viewed as a vendetta to prevent the distribution of Amy's estate."

Turner declined to comment for this story.

Records show she is still a state-certified psychiatrist with a practice.

However, state law strictly prohibits psychiatrists from having physical contact of a sexual nature with a patient.

The American Psychiatric Association also states it's unethical for a practicioner to have a sexual relationship with a current or former patient because "the inherent inequality in the doctor-patient relationship may lead to exploitation of the patient."

It's unclear whether Turner faces any disciplinary action over her relationship.

The state Health Department, which has the power to sanction physicians over misconduct, said it is prohibited from confirming or denying whether a doctor is or has been the subject of an investigation unless public charges have been made or public final action has been taken.

Amy Blumenthal moved to the city from Dallas in January 2010. By May, she was running low on her psychotropic medication and frantically searched for a psychiatrist to treat her.

Turner agreed to see her as a patient that June.

For the next six months, Amy went to Turner three to five times a week for talk therapy sessions, according to court documents filed by Randy. Amy also saw a pharma-psychiatrist to assist Turner "in managing Amy's substantial and ever-changing drug cocktail," her brother says.

By October 2010, Amy had engaged in 50 to 100 hours of therapy with Turner, costing $20,000 to $40,000, according to Randy.

But that professional relationship flew out the window when the psychiatrist fell head over heels for Amy, Randy claims.

Sometime between Oct. 29 and Nov. 26, 2010, Turner called Amy to say she was in her neighborhood and asked to come over to her home. When Turner arrived, she gave Amy a "firm ultimatum" to start a romance, according to Randy's affidavit.

Even though Amy never once asked Turner a personal question during their therapy session, she agreed to the proposition and was soon introducing Turner as her girlfriend, the affidavit says.

During the next few months, "Dr. Turner continued to wield strong power over Amy, quickly moving into Amy's $5 million apartment (from a small, ground-floor rental unit) and, starting almost immediately (through a succession of wills and trust amendments), attempting to receiver her entire estate — a fact which only came to light after Amy's death," Randy says in his affidavit.

He added that in 2013 Amy loaned $1.35 million for Turner to buy a country home in response to "an ultimatum from Dr. Turner that, without a respite in the country, she would need to work on Fridays."

During the course of the relationship, Amy never saw another psychiatrist for talk therapy sessions, relying only on a monthly meeting with a pharma-psychiatrist who solely prescribed her drugs, Randy says.

Her mind also deteriorated with an insurance company eventually approving her for mental disability payments, her brother says. She also expressed concerns to Randy about Turner frequently calling her ex-girlfriend.

Randy, who also runs a swimwear line with his wife, declined to comment on the case. Nor did he respond to a question about the cause of Amy's death.

Turner has also petitioned a judge in Manhattan Surrogate's Court to compel Randy to release money in Amy's trust that he had been investing through his hedge fund. She claims that he has refused to release the funds that are rightfully hers and fears that he may be mishandling the money.