US actor Sylvester Stallone will narrate a new Rocky documentary to be released on-demand on June 9.

The documentary, '40 Years of Rocky: The Birth of a Classic' goes behind the scenes looking at Stallone’s self-created role in the highly successful Rocky series from 1976-2018.

The original Rocky film had a budget of $1,000,000, but brought in $225,000,000 through box office receipts and received ten Academy Award nominations. 

Director Dwayne Johnson said: "The documentary is a golden nugget for ‘Rocky’ fans and casual audiences alike.

“It’s a charming piece of film history narrated by Rocky himself, Sylvester Stallone, and will give audiences an intimate, and at times, emotional experience.

"We’re proud of the film, and audiences can expect new stories and new footage that they’ve never seen before in a blend of director John Avildsen’s home movies, rehearsal footage, and behind-the-scenes footage from the making of the ultimate underdog film.”