Work has started on "This Is Us" season 2 in the last few weeks. Hollywood star Sylvester Stallone, who nabbed a guest spot back in July, recently posted a photo from the set of the NBC drama.

The "Rocky" star will play himself in the new season of "This is Us." He will be working alongside Kevin (Justin Hartley) whose own father Jack (Milo Ventimiglia) idolized the action star.

In the show, Sylvester Stallone and Kevin are supposed to be doing a big war movie together with Ron Howard, who will also play himself.

According to Entertainment Weekly, Sylvester Stallone will stand as a father figure to Kevin.

He will impart some wisdom on "life and acting and memory and aging."

Sylvester Stallone's "This is Us" appearance, however, has been set for one episode only. It will likely be the first or second airing of season 2.

Milo Ventimiglia helped convince Stallone

The "Rambo" star agreed to this brief but special part due to "This is Us" star Milo Ventimiglia (Jack). The latter told Jimmy Kimmel on his late night show that he spoke with Sylvester Stallone personally about appearing on "This is Us." Both actors have a history as Ventimiglia played Stallone's son in the "Rocky" movies.

"His involvement was a very big part of my character’s storyline, of Jack’s storyline, which meant a lot to me because Sly is one of my idols," Ventimiglia said.

Season 2 will celebrate the big three's 37th

"This is Us" season 2 will open with the big three -- Kevin, Kate (Chrissy Metz) and Randall (Sterling K. Brown -- celebrating their 37th birthday, according to Variety. While Kevin has his big movie, Kate will embark on her singing career just like her mom Rebecca (Mandy Moore). Randall, on the other hand, will explore adoption options with his wife Beth (Susan Kelechi Watson).

In the show's 80s timelines, however, "This is Us" season 2 will delve with the aftermath of Jack and Rebecca's separation as shown in last season’s finale. But Milo Ventimiglia revealed that the couple will try to find their way back to each other.

The big death mystery

Jack's death has been the big mystery through the first season of "This is Us." The actors revealed that there will be more revelations this upcoming season.

But if viewers will look into the details of each episode, they can piece together some clues already.

Fans assumed that Jack eventually drove to alcoholism and depression, which resulted in his death. The stars, however, won’t confirm if the speculations are true. Fans will have to tune to “This is Us” when it returns on Sept. 26 on NBC.