For four months, Cyrus Arnold had a front-row seat to some of the greatest minds in comedy, and he relished every second. But when his friends learned about his role in "Zoolander 2," they were less interested in his work with Ben Stiller or Will Ferrell and more interested in the 20 minutes he spent hanging out with Justin Bieber.

"That's all they really cared about," Arnold told Headlines & Global News exclusively about his meeting the pop idol. "But if you know who Will Ferrell is, it's a really big deal to spend a month [filming] with him. It's more of a big deal than meeting Justin Bieber."

Arnold stars as Stiller's son Derek Zoolander Jr. in the comedy sequel. Unlike his male model father, Derek Jr. is an intelligent young teenager who is embarrassed by the idiotic things that come out of his father's mouth while Derek Sr. can't understand how his chubby son isn't obsessed with looking good like him.

"[Derek Sr.] has this thing with people with weight. If you're not good looking, it's not really that you're a bad person but you don't have that many intentions in life and so he doesn't treat me like a son, like a real son, and that upsets my character," the 13-year-old actor said.

Casting for Derek Jr. came down to three boys, and Arnold almost lost out due to his slimmer figure. Stiller wanted a heavyset kid, so the young actor did what he needed to do to win the part - he put on 15 pounds, a much easier feat than he was told.

"They really wanted a heavy kid, and I gained so much weight. People say it's hard, but it's really fun. I mean, you have to eat. People would say, 'Oh, eat this pizza,' and I'd be like, 'OK!' There was no sweat about it," he enthused.

In an example of how far celebrity transcends generations, Arnold had to reference Stiller and co-star Owen Wilson's movies targeted at younger audiences for his friends to know who he was working with. The youngsters were more familiar with Stiller's work in "Night at the Museum" rather than "Tropic Thunder" and recognized Wilson's voice as Lightning McQueen in "Cars," not his many star turns in Wes Anderson films.

Only one man had Arnold laughing so much he couldn't get through a scene. Ferrell's mastery of improv had his co-star practically laughing on the floor during their scene together.

"I couldn't put up with how funny he was. I broke character once in the whole movie, and that was with Will Ferrell," he said.

Stiller had his movie son watch the original "Zoolander" a total of four times - twice before he got cast and twice after. They also spent an entire day working on his interpretation of Derek Zoolander's signature look, Blue Steel, a skill much harder than it looks.

"I haven't even perfected it yet. That's how specific that look is. You think all you have to do is stick your lips out and think sexy. No! It's really hard to describe," Arnold said.

The California native and his good friend Jake Brennan (Netflix's "Richie Rich") may one day succeed the likes of Stiller, Wilson and Ferrell as the funniest guys in comedy. The two child actors, who first worked together on an episode of Nickelodeon's "Sam & Cat," are working on developing a new web series satirizing the little things in life that annoy them.

In the meantime, be sure to catch Arnold in "Zoolander 2," out in theaters now.