Sylvester Stallone and Jennifer Flavin. Picture: Bang Showbiz

'Rocky' star Sylvester Stallone is set to play himself in the hit NBC show 'This Is Us' as a mentor for Justin Hartley's character.

The 71-year-old action legend - who is married to Jennifer Flavin - will serve as a mentor to Justin Hartley's bachelor character Kevin in the hit show and will be helping him through feelings he has about his father Jack (Milo Ventimiglia) who died at the end of Season One.

Executive producer of the show, Dan Fogelman said: "Kevin is shooting a big movie and we needed his big co-star and Sly Stallone is coming to do a huge part on the show as Kevin's co-star and father figure in the film he's shooting."

Stallone is only set to appear in one episode but Dan has hinted his role could be stretch on throughout the season.

Dan said: "We have a great script for him. I think it's going to be really, really exciting."

Milo, 40, worked with Stallone in the 2006 'Rocky Balboa' movie playing Rocky's son and the two remained close friends and it's reported Milo helped him get cast in the NBC show.

Season Two of the show is set to deal with Jack's death and the show creator said any questions will get answered.

He said: "If that is a question that has haunted people, over the course of the second season, they will get all the answers they want.

"The first episode has a big giant piece of the puzzle that will potentially set the internet abuzz and hopefully give some momentum toward that storyline."

In July, Stallone teased a sequel to the hit movie 'Creed' and shared a photoshopped movie poster on his Instagram account in which Apollo Creed's son Adonis Creed (Michael B. Jordan) stands toe-to-toe with his Ivan Drago (Dolph Lundgren), the Russian pugilist who killed his father in the 1985 film 'Rocky IV' along with the quote "history will always repeat itself".