Home Alone viewers only just realising Macaulay Culkin's brother Kieran also stars in film

It’s official: We have less than three weeks to go until the big day, and that means we’re all well in the swing of marathoning all our favourite movies and donning our festive PJs.

There’s sort of a ritual when it comes to Christmas, isn’t there?

One night, you’ll cry to Love Actually, laugh to The Grinch and wish you were living the life of Kate Winslet and Cameron Diaz in The Holiday.

Then, as it really gets closer to the big day, you’ll no doubt whack on the Home Alone movies.

Let’s be clear, I’m talking about one and two, not three or four…or five.

The Macaulay Culkin films.

The 1990 film is a staple for around this time, and it’s casting choices were just *mwah*, chef’s kiss.

Macaulay Culkin was in two of the Christmas films (20th Century Studios)

There was a young Macaulay Culkin, Joe Pesci, Daniel Stern, John Heard and Catherine O'Hara.

The first film is undoubtably the best one to come from the franchise.

It follows the story of eight-year-old Kevin McCallister (Culkin) who is accidentally left behind at home when his family leaves for France.

In the beginning of the story, as he had wished that his family would disappear, he's happy to be in charge; but when robbers try to break into his home, he puts his pranks to the test.

While there were five films in total, it was was only Home Alone 2: Lost in New York which starred Culkin again, as the others recast him.

While you might believe that you know everything there is to know about the films, there’s something you completely missed.

Now, Home Alone fans are only just realising Culkin's younger brother, Kieran, was also in the film too.

That’s right, so the next time you pop on the holiday classic on, take a look at Kieran in his first on-screen role.

The 42-year-old later went on to become one of the main characters in HBO hit comedy Succession.

Kieran worked alongside his brother from a young age (20th Century Studios)

What’s even more weird is that while Kieran and Macaulay are siblings in real life, Kieran didn't star as one of Kevin’s many siblings.

Instead, he was actually his younger cousin, Fuller - the one who pees himself.

You get to see him at the beginning of the film, when the family are all eating pizzas during a dinner.

Fuller wears a pair of glasses and 90s dungarees while being told to 'go easy on the Pepsi' as he is known to wet the bed.

Kieran Culkin is more known for his role in Succession (XNY/Star Max/GC Images)

But what’s even worse is that Fuller is supposed to share a bed with Kevin the night before the family all took off to the French city.

However, it wasn’t meant to be as after Kevin and his mother argue, he’s sent to bed on his own, in the attic of all places.

Unknowingly, that would be the last time he would see his family for a while.

Oddly, they didn’t even realise until they’d just gone to board the plane that Kevin wasn’t there.

This then led to a series of events where the family rushed to get back to him, while he was battling with thieves.

It’s a classic.