DNA ancestry sites were key in cracking the case of the 1964 abduction of a newborn boy swiped from a Chicago hospital, a genetic genealogist has revealed.

One of Paul Fronczak’s close relatives submitted DNA samples to several ancestry sites in an attempt to find the newborn, who was snatched from his mother’s hospital room on April 27, 1964, according to genetic genealogist CeCe Moore.

Fronczak was only 1 day old when a woman posing as a nurse took off with him, officials said.

The FBI launched a search for the child that led to an abandoned baby in New Jersey who had ears similar to parents Chester and Dora Fronczak’s missing son.

The couple adopted the child and raised him as their own, but he took a DNA test later on in life proving he wasn’t related to them.

The man who had grown up as Paul Fronczak then set out to find his adoptive parents’ still-missing son, according to Moore. In 2014, she worked with the adopted man to submit a DNA sample from one of his close relatives to Ancestry.com, 23andme.com, MyHeritage.com and FamilyTreeDNA.com.

The sites altogether have around 30 million DNA records from others who voluntarily upload their results and allow users to connect with people who share their genetic ancestry.

She described the experiment as a genetic fishing expedition — but it paid off last year when they finally got a notification through one of the sites that there was a match.

The other Paul Fronczak turned out to be a 55-year-old man living in rural Michigan, she said.

Moore declined to provide more details about the man and his family, citing his privacy.

“The most important thing is that he and his mother have a reunion,” Moore told the Associated Press. “Our greatest wish is for that to happen.”

His mom, Dora Fronczak, is in her 80s and still lives in the Chicago area, while Chester died several years ago, WGN-TV reported.

The FBI declined to confirm whether the case has been solved.

“Several years ago, the FBI reopened the investigation into the disappearance of Paul Joseph Fronczak,” an FBI Chicago spokesperson told WGN-TV. “Our investigation into this matter remains ongoing as we continue to pursue all leads. We ask for privacy for the victims as we continue to investigate the facts surrounding this case.”

With Post wires