Richard Jenkins completely improvised one of the best scenes in Step Brothers

It turns out that one of the greatest scenes in comedy history was improvised.

Few fictional events command the same amount of attention as the f***ing Catalina Wine Mixer in the iconic 2008 comedy Step Brothers, seeing as it's a serious event full of serious people.

Well, that was until Adam McKay's unruly step brothers, played by Will Ferrell and John C. Reilly came in with full chaotic force. And it turns out that our favourite scene from the entire event was entirely improvised by the boys' father, played by Richard Jenkins.

Check out what the actor had to say here:

For those not familiar with the 2008 smash hit, it follows two grown ass-men who live at home and are forced to become step-brothers when their parents marry.

Their initial hatred for each other is turned into an unbreakable 'did we just become best friends' bond, and it's honestly one of the funniest films out there.

In the film, the Catalina Wine Mixer becomes a source of contention, and the brothers, who are trying to start a party planning company, do their best to help pull off an incredible event.

Columbia Pictures

When things don't go their way, their father gives them a pep talk, in which he reveals that he wanted to be a dinosaur when he was young but gave up on his dream far too early.

It honestly had us in tears the first time we saw it, and now we've found out that it was completely improvised.

As Jenkins explained while appearing on The Rich Eisen Show: "It was the dinosaur speech that you talked about. I was sitting there at the Catalina Wine Mixer, and Adam McKay said to me 'go tell Will [Ferrell] and John [C. Reilly] that you wanted to be a dinosaur when you were young.'

"I said 'what are you talking about?' he said 'you know just go tell them.' I said, 'Adam, what the hell are you talking about?'

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"So, it was not scripted, he just came along he said go tell them, so, like, whatever, and I started talking, and both of them kept saying to me: 'that's just not possible, what are you talking about?'

"And I came back home [thinking] that won't be in the movie, and Adam said, 'oh yes, it would.'

"I mean the two of them, Adam, I mean, Will and John are so quick they just they, just you just, you can't keep up."

Yep, so McKay pitched the idea to Jenkins, who ran with it and pulled off one of the funniest scenes in the film.