A renowned orthopedic surgeon at NYU Langone turned into a crazy ex-boyfriend when his office manager broke up with him — hiring gumshoes to tail her and getting her arrested on bogus embezzlement charges, she claims in a new lawsuit.

Dr. John G. Kennedy — who heads the foot and ankle division of the hospital’s Department of Orthopedic Surgery — started barraging Susanne Shafmeister with “egregious and frightening threats and harassment” shortly after their relationship devolved in late 2018, according to the lawsuit filed Friday in Manhattan Federal Court.

But the nightmare ex-boyfriend scenario got even worse when Shafmeister reported the conduct to Human Resources, the suit claims.

The hospital “decided to take every possible step to protect Dr. Kennedy and subjected Ms. Shafmeister to blatant and unconscionable retaliation,” it alleges.

Shafmeister says she filed an HR complaint Oct. 11 and had a follow-up call in a conference room Oct. 15.

After the call, Dr. Kennedy allegedly barged into the conference room, threatening to report Shafmeister to federal authorities for embezzlement if she refused to drop the complaint, the court documents state.

She claims he found out about the call because he’d hidden a recording device in the room.

Shafmeister also claims Kennedy hired private detectives to follow her, and enlisted another doctor at the hospital to let the PI know when she was leaving work.

“Hey buddy. Dr Kennedy needs you to text scott the detective when shafy leaves the office today,” read text messages included in the lawsuit, that were allegedly sent by the doctor Kennedy enlisted to another doctor.

“Can u do that? without her knowing of course,” the texts say.

Shafmeister “was concerned about her safety… [and] was so scared that Dr. Kennedy would break into her home and hurt her that she moved out,” of her downtown Manhattan apartment, the suit states.

The couple began dating around 2005, shortly after Shafmeister moved to the US from her native Germany. About a year in to their relationship, Kennedy hired Shafmeister as office manager at his private practice, and she worked there until 2018, when they both moved to NYU Langone, per the suit.

By the end of 2018, Shafmeister had broken things off after finding out that Kennedy dated multiple other women, and had even married one gal pal, all while seeing her. Kennedy claimed he’d wed the woman because she had terminal cancer and her dying wish was to tie the knot with him, the court documents state.

Still, Shafmeister agreed to go work with her ex at the hospital to benefit her career, all while hoping he’d keep things professional, the suit says.

“Unfortunately it soon became clear that Dr. Kennedy had not come to terms with Ms. Shafmeister’s decision to end their personal relationship, and began subjecting [her] to discriminatory harassment and retaliation in the workplace for her decision to end their relationship.”

His conduct allegedly included yelling and berating Shafmeister, forcing her to talk through their break-up at the office and repeatedly threatening to can her.

In the spring of 2019, “Kennedy became increasingly obsessed” with Shafmeister’s new boyfriend, making anti-Semitic comments about the beau, forcing co-workers to show him pictures of the pair on social media and riffling through Shafmeister’s desk at work, the suit claims.

At one point, Shafmeister says she asked Kennedy for advice about not receiving a bonus that had been promised to her upon her hiring, and he told her to write herself a $12,000 check from his private practice’s business account, the suit alleges.

But after she did, Kennedy allegedly claimed Shafmeister had robbed him, yelling at her that: “Now I’ve finally got you. You have committed a felony and I will report you to the feds. You will end up behind bars and I will have you deported,” the suit claims.

“I don’t give a sh-t if you end up with your two dogs on the street,” he told her, according to the lawsuit.

Shafmeister, who is a legal resident but not a US citizen, eventually gave him back $10,000 and he allowed her to keep the remaining $2,000, per the suit.

“After Dr. Kennedy made multiple failed attempts to coerce Ms. Shafmeister to rescind her [HR] complaints, he finally made good on his threat,” the suit states.

Shafmeister was arrested by the NYPD on Nov. 18 and charged with grand larceny. A temporary order of protection was also issued against her, after Kennedy allegedly told cops he feared for his safety.

After the arrest, Kennedy allegedly told co-workers Shafmeister didn’t work at the hospital anymore and her desk was cleared.

HR then asked her to come in to meet — but she responded that she couldn’t because of the order of protection and criminal charges, the suit states.

The department then allegedly sent her a list of questions to answer, including “the dates and locations of certain times Ms. Shafmeister had been ‘intimate’ with Dr. Kennedy,” the suit says.

When she eventually came back to work, Shafmeister learned her job description was changed and she was stripped of managerial duties, “clearly an act of retaliation … for having the courage to bring forth her complaints of discrimination,” the court docs allege.

She’s asking for damages to be determined at trial, costs and attorney’s fees and for her old job back. Her next court date in the criminal case is January 17, 2020.

“She’s extremely committed to seeing this through,” said Shafmeister’s attorney, Michael J. Willemin. “She went to NYU hoping they would do something to stop this and remedy the situation and they did nothing … and they still haven’t done anything except move her from her responsibilities, and, as far as we know, allow [Kennedy] to continue doing his work.”

A spokesperson for NYU Langone Health said the department doesn’t comment on pending matters. Kennedy didn’t return a phone call on Monday.

Additional reporting by Priscilla DeGregory