If you're a parent then at some point you will no doubt have encountered one of the Biff and Chip children's books.
A mainstay of the National Curriculum, the books have helped children learn how to read for more than 30 years and are used in 80 per cent of Britain's primary schools.
But despite them being read by thousands of families, it seems something has passed them by - and it's pretty much blowing parents' minds.
That's because Biff and Chip aren't actually called Biff and Chip. They are indeed Elizabeth and David. And Kipper isn't even Kipper, he's Christopher.
Jo Evans tweeted a photo of a page from one of the Oxford Reading Tree books detailing their real names - and it's been somewhat of a revelation.
The book states: "Biff and Chip are twins. Biff's real name is Elizabeth. Chip's real name is David. So why are they called Biff and Chip?
"Because when Kipper was little he couldn't say Elizabeth or Beth. He said Biff. And he couldn't say David. He said Chip.
"Chip doesn't sound like David, but that is what Kipper said and everyone laughed so the nicknames stuck!".
It adds that Christopher couldn't say his own name when he was younger and it sounded like Kipper - 'Dad decided that the name Kipper suited him so now everyone calls him Kipper'.
In her tweet, Jo said: "How old were you when you found out Biff, Chip and Kipper were actually called Elizabeth, David and Christopher?
"And don’t say 4 years old!!! I was precisely today years old. Now wondering what else is a lie!!!"
Her tweet has been shared nearly 5,000 times since Saturday, with others publishing it on Facebook.
Primary school teacher Kimberley Evans' Facebook post has quickly gone viral, amassing 21k shares since Sunday morning.
She said: "OK, why did they not teach us this at university? This has blown my mind. I have been a primary school teacher for 20 years and did not know this! Tell me I'm not the only one ...
"Thanks to @JoEvans1976 for the original photo. If you know her please tell her I want to send her a thank you gift!!!"
Thousands of people commented on her post, sharing their amazement over the siblings' real names.
One said: "I can’t think how many hundreds of children I have taught and heard read those names - and I’ve never known that!!!"
While another added: "I always wondered why they called them by those names."
