"Woman Gives Birth To Children, Discovers Her Twin Is Actually The Biological Mother, But She Is Technically Her Own Twin," the convoluted headline on the Opposing Views site declares.

You could be forgiven for thinking this was a Weekly World News-style tale, in the same family as Woman Gives Birth To Alien. But this bizarre story is actually true.

Opposing Views sums it up:

A Washington state woman was shocked when she was told that the children she gave birth to were not her own. It turned out that her twin was actually the biological mother of her children, and this only led to more confusion because she didn't have a twin. In the end, it was discovered that the woman was in fact her own twin, confirmed by doctors to be a rare medical condition.

The story of Lydia Fairchild, reported by ABC News back in 2006, has resurfaced just this week — largely because it's so irresistibly twisted.

How it began

In 2002, Fairchild, a mother of two with one more on the way, applied for public assistance. To make sure that her former boyfriend, Jamie Townsend, was actually the father of the children, the kids were all subjected to a paternity test.

And that's where things got weird.

The DNA test confirmed that Townsend was the father, but showed that Fairchild was not the mother. After the state — suspecting Fairchild or welfare fraud or worse — monitored the birth of her third child, they found that Fairchild was also not the genetic mother of the child she had just given birth to.

"Prosecutors were dumbfounded," Sam Kean wrote in Psychology Today. "One of them began searching the medical literature and came across an eerily similar case from 1998" involving a 52-year-old woman named Karen Keegan.

Mystery solved

Keegan's adult sons underwent genetic testing when their mother needed a kidney transplant, to see if they might be a match. But then a test revealed that their genetic material did not overlap with their mother's at all.

A British documentary, The Twin Inside Me, explains what happened next:

A series of tests had shown that Karen was a 'chimera' — a term derived from the Greek mythological creature that was a mutation of more than one animal. Shortly after conception, the female egg that was to become Karen became fused with another female egg. As a result, the fused egg contained two entirely separate DNA blueprints which were combined in Karen. This means that, biologically, Karen is more than one person.

DNA is supposed to be our unique biological calling card — it's why it is sometimes so crucial in criminal investigations. But when a person is a chimera, they have more than one DNA signature.

A cheek swab may make it seems like they are one person, while cervical cells — which eventually linked Fairchild to her children — could make it seem like they are someone else entirely.

You might be your own twin, too

While the stories of Lydia Fairchild and Karen Keegan seem like once-in-a-lifetime oddities, the basic biology of chimerism — when one person has the cells of two or more people in their body — is not as unusual as you might think.

"Firm numbers remain elusive, but most—if not all—humans are probably a little chimeric, since mothers and fetuses commonly exchange cells during pregnancy," Kean writes.

One twin completely absorbing another in the womb, as likely happened with Keegan and Fairchild, is probably rare. But it's becoming more common, as in-vitro fertilization increases the chance of twins, and therefore chimerism as well.

"A chimera from one male and one female twin can become a hermaphrodite; if twins are the same sex, the child might have patches of skin or eyes of different colors, but otherwise will probably appear normal," Kean writes. "In the absence of extensive DNA testing, he or she will probably never know."