This is one story you definitely have never heard of. A recent case study revealed that after a man failed a paternity test, it was discovered that part of his genome actually belongs to his unborn twin.

It turned out that the biological father of the man's child is actually the man's brother  - "who never made it past a few cells in the womb." IFLScience reports:

"It all starts off with a couple in the U.S. who were having trouble conceiving their second child. They decided to seek help and went to a fertility clinic, where eventually intrauterine insemination was performed. This involves washing and concentrating sperm before inserting it directly into the uterus of a woman around the time of ovulation to boost the chances of fertilization.

"The assisted conception worked, and nine months later the happy couple welcomed a baby boy into the world. But then things started to take a turn for the weird. Testing revealed that the child's blood type didn't match up with his parents'."

"Both parents are A, but the child is AB," said Barry Starr of the Department of Genetics at Standford University. "There are rare cases where that can happen, but their first thought was that the clinic had mixed up sperm samples."

To shed more clarity on the situation, the couple decided to take a paternity test - which revealed that the man was not the child's biological father. After taking a second test, the results came out the same.

Although mixed up samples seem to be pretty feasible, the clinic only had one other intrauterine insemination case at the same time.

However, the other couple involved an African-American man - which helped ruled out that it indeed wasn't a case of mixed samples, since the child's physical appearance didn't match.

The couple's lawyer then decided to contact Barry Starr, who suggested a more powerful test - the over-the-counter 23andMe genetic service - for the couple to take. Apparently, this test can help look at family relationships.

The results showed that the child's father was actually his uncle, the man's brother. Of course, Starr decided to dig in deeper - thinking that the man could possibly be a "human chimera" or a person with different genomes.

DNA samples were taken from the cheek of the father - which was used for the initial paternity tests - as well as his sperm. It was found that the cheek cells did not match with the child, although the sperm sample proved to be something else.

A "major" genome was found - which supports the human chimera theory. Turns out that the genome accounted for approximately 90 percent of the sperm cells, while a "minor" genome only represented an estimated 10 percent  and was found to match the child's DNA.

Barry Starr claims that "the father is the fusion of two people, both the child's father and uncle."