Identical twin sisters who married identical twin brothers gave birth to sons that are brothers and cousins at the same time.
Briana and Brittany Deane, 25, from Virginia in the US, tied the knot with Jeremy and Josh Salyer before falling pregnant around the same time last year.
Brittany gave birth to Jett, who turned one in January, while Briana had Jax, who celebrated his first birthday a few months later in April.
Quartenary twins
But despite being born a few months apart, they are technically 'quartenary twins' - which means they're cousins and genetic brothers because of their DNA.
And their parents' marriages are known as 'quartenary marriages'.
Quartenary phenomenon
During an interview with NBC News, Brittany explained the quartenary phenomenon before revealing there are 300 other twins with the same unique make-up worldwide.
You might think you're seeing double, but check out the two families' Instagram account.