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A woman in Wisconsin is suing her fertility doctor after discovering he fathered her child instead of the 'healthy young medical school student' donor she was promised, a shocking lawsuit has claimed.

Mary Ellen Lukezich, 71, was a patient of Dr Frederick Dettmann over 40 years ago when she was artificially inseminated with a donor's sperm.

Now, Lukezich and her son, 43-year-old Joseph Laedtke Heider, are suing Dettmann, now 91, after they discovered Heider allegedly had nine other half-siblings fathered by the doctor, NBC reports.

'Words cannot fully express what it feels like to learn that your entire identity is built on a lie,' Heider said at a news conference in June, ABC-affiliate WISN reported.

In December 2024, Heider submitted his DNA to Ancestry.com and made the shocking revelation that Dettmann was his biological father, the lawsuit obtained by the outlet claimed.

'Upon tracing these DNA connections, Joseph identified a direct genetic link to Dr Dettmanns' family; that upon information and belief, this genetic information established that Dr Dettmann is Joseph's biological father,' the suit said.

Lukezich had been a patient of Dettmann's in 1982 and, after medication and surgical treatments proved unsuccessful, he recommended she try artificial insemination, the outlet reported.

According to the filing, Dettmann told her that the donor would be an anonymous 'healthy young medical school student.'

Mary Ellen Lukezich, 71, and her son, 43-year-old Joseph Laedtke Heider, are suing Dr Frederick Dettmenn claiming that Heider had nine half-siblings fathered by the fertility doctor

Lukezich was a patient of Dr Frederick Dettmann over 40 years ago when she was artificially inseminated with, what she believed was, the sperm of a student donor

The lawsuit was filed on August 6 by their attorney Al Foeckler, seen above, with the Wisconsin Health Care Liability Insurance Plan and ABC Insurance Co also listed as defendants

The lawsuit alleged that Dettmann, instead, used his own sperm during the procedure which led to the birth of her son, Joseph, the following year.

But the family was left unaware of the switch until Heider submitted his DNA to Ancestry.com.

'I got an email from Ancestry, which is the company that I ordered the DNA test from, that I had a half sister,' he told NBC News. 'And so when I went into the DNA results and the relationships, I had noticed that there was multiple half siblings that it had suggested that I was related to.'

When he later connected the potential relatives to his mother's former OBGYN, his mother was flabbergasted.

'What he did was incomprehensible and it was such a betrayal of trust that I just wanted to make sure that if I have the opportunity to hold him accountable for the pain that he caused my mom and the things he put her through, that maybe she didn't even know at the time,' Heider said.

Lukezich also said that when she learned what the doctor allegedly did to her, she felt violated.

'I feel like I've been raped,' she told the outlet. 'And it's not right. And I want other women to feel OK about coming forward with this.'

The lawsuit was filed on August 6 on behalf of the mother and son by their attorney Al Foeckler, with the Wisconsin Health Care Liability Insurance Plan and ABC Insurance Co also listed as defendants.

According to the filing, Dettmann told her that the donor would be an anonymous 'healthy young medical school student'

'These families come to fertility doctors at their most hopeful and their most helpless time,' Foeckler noted at a news conference announcing the suit

'Trusting completely in the physician who holds their dreams of parenthood in their hands. Dr Frederick Dettmann preyed on that desperation. He exploited that trust.'

Since that press conference, Foeckler said multiple women have contacted him to share their own uncomfortable interactions with Frederick Dettmann dating as far back as the 1970s.

'There is no question in my mind that this man was a serial predator of women,' he said.

The since-retired doctor denied any wrongdoing in a statement submitted by his legal team on his behalf.

'The events referenced are alleged to have occurred almost 50 years ago. Dr Dettmann has no independent recollection of the individuals making these allegations and is unaware of any evidence supporting the claims being asserted,' the statement said, according to WISN.

The since-retired doctor denied any wrongdoing in a statement submitted by his legal team on his behalf

According to Whitefish Bay police records, Dettmann had been accused of assaulting a woman during a gynecological exam in 1985, TMJ 4 reported.

No charges were issued, citing that proving the assault would be 'too difficult,' according to the outlet.

All of the records about the case would have since been destroyed under record retention laws at the time, Whitefish Bay Police Chief Patrick Whitaker told NBC.

The police records that are available, though, note that the sexual assault complaint was reported to Wisconsin's medical licensing board, which closed the case in 1986 after a consideration of the facts and a vote.

A spokesperson for the Wisconsin Department of Safety and Professional Services told NBC News it does not have records of closed complaints from that long ago.

Gaynor has since noted that Dettmann was 'never sued, disciplined, investigated, had his licensure challenged, nor were any ethical complaints ever made against him.'

The doctor retired in the 1990s and now lives in Arizona.

The Daily Mail reached out to Wisconsin Health Care Liability Insurance Plan and ABC Insurance Co. and attempted to reach Lukezich, Heider and Dettmann for comment.