"How can you get pregnant while you're already pregnant?" Sam Burgess is beyond baffled.

Up until today, I thought I knew just about everything there was to know about twins.

Firstly, because I am a twin. And secondly, because I have twin brothers. We have a twin club and no-one else is invited. Not even mum and dad.

I know that as a kid being called “twinny” made me want to punch grown adults in the throat.

I know what it’s like to be pinched on the arm before someone laughs so loud a little bit of spittle gets in your eye, and they exclaim, “DID YOUR TWIN FEEL THAT?”

No. No they didn’t.

I know how embarrassing it is to walk past a mirrored corridor at uni and say, “Hey Clare, I didn’t know you were at uni today!” before slowly realising she most definitely is not. 

I know what it's like to have someone excitedly tell you, "No you're identical! You're definitely identical!" when identical isn't, like, a matter of opinion. It's about an egg. And guess who wasn't there 26 years ago when that egg split, huh? You. You weren't there.

I thought I knew all the things - and so did the Burgess brothers.

They are, second to my siblings and I, perhaps the most iconic sporting families in the country.

The eldest of the four, Luke Burgess, currently plays professional Rugby League in France, while twins Tom and George play alongside their older brother, Sam Burgess, for the South Sydney Rabbitohs.

As Sam, Tom and George were grilled by comedian Katie Burch for Who's in The Car, Australia's version of Carpool Karaoke minus the singing (thank God), Katie explained that her husband is also a twin. But he's not your average twin. He out-twins us all.

Her mother-in-law fell pregnant, while she was already pregnant.

My mum talks about how she had two sets of twins in two and a half years. Post continues below. 

And Sam Burgess cannot. He just can't understand how that is a thing that happens and it's hurting all of our brains.

"She got pregnant, while she was pregnant?" he repeats.

You can see Burgess' brain thinking, "but... twins are... the same. Same time. One pregnancy. At once."

He decides to restate the question, to clarify, "She got pregnant, while she was pregnant?"

YES, Sam. CORRECT.

After a few seconds he reflects, "That has just blown my tiny mind," and goodness gracious mine too.

How pissed off would you be? 

If I had to identify the best measures of contraception, I would say already being pregnant would be one of them.

But no. Life has a way of kicking you right in the ovaries - just when you least expect it.

The phenomenon is known as "superfetation", and it occurs when the implantation of the first embryo is delayed, meaning there is no initial spike in hormones.

The pregnancy hormones are responsible for shutting down a woman's reproductive system, so if that doesn't happen, it's entirely possible for her to ovulate during pregnancy.

It's even possible for a set of twins to have two different fathers, which is potentially the funnest fact we've learned this year.

Look, Sam Burgess is still confused and to be honest so am I.

You can watch the full video above. Who's In The Car is a new online video series by Youi car insurance.