Justin Hartley works with Sylvester Stallone on 'This Is Us'

We all know and love Justin Hartley as Kevin on "This Is Us," and to the delight of millions of people, the show is back for a second season. Hartley stopped by BUILD Series NYC to chat about the new season. One memorable moment Hartley had this season was working with the legendary Sylvester Stallone. In this new season, we can find Kevin trying to redefine himself and become a better man. Kevin gets the opportunity to be apart of a Ron Howard film, and Stallone (who is playing himself) is Kevin's co-star.

Stallone's presence on "This Is Us" was necessary to make the scene work.

"His (Kevin) co-star needs to be this larger than life movie star. So because we operate in this world where it is Ron Howard's film we need a larger than life huge movie star. So it's not necessarily like would it be cool if we got Sylvester Stallone on our set, we kind of need him, he helps tell the story. When that man walks out on set, then you're like 'oh, this is a legit film.'"

While on set, Stallone was the humble class act that Hartley felt he could learn from.

"I think he leads by example. I don't know the man very well, but I can tell you what it seemed like when I was around him. He is very prepared, very smart, very professional, and funny. He immediately made you feel like you were just talking to one of the guys."

Hartley first met Stallone at the gym and Stallone showed him some useful tricks.

"I meet him at the gym, and he was giving me a couple of pointers on how to get a quick pump up before a scene. I didn't know you can literally jack yourself up for a scene in 2 minutes."

You can watch Hartley on "This Is Us" every Tuesday night on NBC. You can also catch Stallone on "This Is Us" in next week's episode on October 10th.