The Terminator joined the brothers on their "New Heights" podcast this week ... and before the show really got going, he told the guys he was positive they were both in Tinseltown this week because they're trying to make plays to get onto the silver screen.

"I'm not stupid," he said after noting the two -- who usually do their podcast from different cities -- were together in the City of Angels. "There's a reason."

If Arnie's right, neither Kelce brother was willing to admit it on the show -- as they just laughed through Schwarzenegger's commentary.

But, that didn't stop Arnold from continuing his speculation -- because he added, "You guys have it lined up. You just don't want to give it away right now. I know the way this works."

The Kelces changed the topic back toward Arnold quickly, but later in the show, Schwarzenegger gave the guys advice on how to pick roles if and when they ultimately get into the field.

Arnold told them it was important to make sure the script is good first and foremost, saying, "What's not on the page is not on the stage."

And, the guys sure seemed to soak in the words -- an indication that maybe Arnold's theory wasn't wrong.

To add even further fuel to the fire, to end the program, the guys joked about starring alongside Schwarzenegger in a "Conan The Barbarian" reboot.