The human body is truly an amazing thing. Just when you think that becoming pregnant with your own child while carrying a child belonging to someone else (by surrogacy) couldn't ever happen - it does. And no, this is not the plot of a new sci-fi film.
Californian mum Jessica Allen, thought she was carrying twins belonging to a Chinese couple who she agreed to be a surrogate for.
In December of last year, Allen gave birth to two baby boys and handed them over to their parents.
It wasn't until she saw a photo of the growing boys sometime later that she noticed something wasn't right. Telling ABC News, Allen noticed that one of the babies had distinctly Chinese features while the other did not.
"You know, obviously they were not identical twins," she said.
Allen and her husband, Wardell Jasper, later learned through DNA testing that one of the boys was biologically theirs. The couple then entered into a long and emotional legal battle to get their son back.
"I carried my own child and I didn't know he was mine," Allen told ABC News through tears.
The couple was finally granted custody of their little boy in February and they named him Malachi.
While it's wonderful news that Malachi is with his biological mum and dad, the question is left begging - how does something like this happen in the first place?
In a word, superfetation.
Superfetation is a medical phenomenon where a woman continues to ovulate after becoming pregnant. It's extremely rare but in such cases fertilisation and implementation of a second embryo can result in two babies with different gestational ages, and in Allen's situation, two different sets of genetic parents.
The couple, who were married in April this year, explained to the New York Post that they weren't planning on expanding their family so soon, but now that they have Malachi in their lives they would not have it any other way.
"We treasure Malachi with all our hearts," the happy mum said.