A woman gave birth to twins with two different dads after having sex with both men on the very same day.
A woman gave birth two twins with two different fathers
The 19-year-old mother is only the 20th known case of what is known as "heteropaternal superfecundation".
The man she thought was the biological father of both of her boys took a DNA test and the result came back as positive for only one of the children.
The unnamed Brazilian woman said: "I remembered that I had sex with another man and called him to take the test, which was positive. I was surprised by the results.
"I didn't know this could happen and the babies are very similar."
The woman's doctor Tulio Jorge Franco said: "Two eggs from the same mother are fertilised by different men.
"It happens once in a million. I never imagined I would see such a case in my life."