A Brazilian woman trying to find out which of sexual partners fathered her twins got a shock when both tested as the dad. 

The 19-year-old from Minerios, Brazil, told local TV news outlet Globo she “didn’t know this could happen”. 

It turns out she had a “one-in-a-million” condition called heteropaternal superfecundation, where two of her eggs were fertilised by different men, according to her doctor.

That makes the twins genetically half-brothers, even though they’re also twins. 

They were eight months old before the woman started to have doubts about the twins’ paternity. The man she thought was the father only tested positive for one of the kids, prompting the hunt for the others’ dad.

One of the men has registered himself as the legal father of both, Globo reported, but it’s not clear which.

“He takes care of both of them, helps me a lot, and gives them all the necessary support that they need,” she told Globo.

The boys are now 16 months old. Though common in cats, dogs and Greek mythology, heteropaternal superfecundation is rare in humans.