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 passed the same birthday a few months later in April.
But despite the time between the two births, they are technically " quartenary twins " - meaning they're cousins and genetic brothers because of their DNA.
The two families - who share an Instagram page - shared news of the genetic phenomenon with their 219,000 followers.
Clearing up any confusion, one user wrote: "Identical twins share the same DNA. When two sets of identical twins marry, it makes their kids genetic sibling."
"A pair of identical twins marrying identical twins is called a 'quaternary marriage."
Another chimed in, saying: "Identical twins share the exact same genetic material, egg/sperm and all (while fraternal twins are conceived from a different egg and sperm)."
A third quipped: "Basically impossible for either to be charged with a crime?"
Others urged the couples to "please" undergo a DNA test to "see if its [sic] true."
During an interview with NBC News, Brittany explained the quartenary phenomenon before revealing there are 300 other similar twins with the same unique make-up worldwide.
She said: "They were born to identical twin parents less than nine months apart. Twins married to twins who both have babies at the same time."
Brittany announced Jett's birth on January 21 before dad Josh posted an emotional photo of the new mum with her boy.
He captioned the image: "Brittany did wonderfully in delivery.
"I am so proud of them and excited to be Jett's dad!"
Months later Jeremy, Briana's husband and Jax's dad, captioned their own happy photo, saying: "I am so proud of my beautiful wife, Briana, and how well she did.
"She was so strong and brave and did an amazing job.
"I am thankful that our boys will grow up together!"
Meanwhile, a Brit mum has shockingly revealed she is regularly questioned about whether her twins are "both hers".
Chantelle Broughton, 29, gave birth to two babies of 'totally different' skin colours this April, and said she was left shocked after being given the newborns after birth.
Ayon and Azirah - who were born at Nottingham City Hospital - have completely different features to one another, report Nottingham Live.
Her son, Ayon, was born with fair skin and green eyes; while her daughter, Azirah, had dark skin and brown eyes.
Recalling the moment she was handed her newborns, Chantelle said: "It was a shock how different they appeared, they're unique.
