Jason Isbell and Sturgill Simpson board Scorsese's Killers of the Flower Moon

Jason Isbell and Sturgill Simpson have joined the cast of 'Killers of the Flower Moon'.

The country music stars are the latest names confirmed for Martin Scorsese’s epic Western, which will also star Leonardo DiCaprio, Robert De Niro, and Jesse Plemons.

According to Deadline, Isbell, 42, will make his acting debut as Bill Smith, an “adversary” to DiCaprio’s Ernest Burkhart.

While 'Queen & Slim' star Simpson, also 42, has been cast as “infamous rodeo champion and bootlegger Henry Grammer.”

'The Twilight Saga: Eclipse' actor William Belleau and 'The Irishman's Louis Cancelmi have also boarded the flick as Osage rancher Henry Roan and hustler Kelsie Morrison, respectively.

What's more, Jack Fisk has been added as a production designer.

The filmmaker's previous credits include 'There Will Be Blood', 'The New World', and 'The Revenant'.

The Apple Original movie is based on David Grann's best-selling book of the same name.

The Osage Nation were the richest people per capita in the world and were killed one by one after oil was discovered on their land. As the death toll increased, the newly-created FBI took up the case and unravelled one of the most monstrous crimes in American history.

Plemons plays the lead FBI agent Tom White in the investigation, which came to be known as the Reign of Terror.

And Lily Gladstone stars as Mollie Burkhart – an Osage married to Ernest (DiCaprio), the nephew of a powerful local rancher portrayed by De Niro.

Scorsese is directing and producing the movie for Apple with Eli Roth writing the screenplay. A release date is yet to be confirmed.

The Hollywood legend recently revealed that the coronavirus pandemic actually benefited 'Killers of the Flower Moon' despite the project being subject to numerous delays as a result.

He said: "I feel as we're playing with it now, it's had a layer in, along with the actual main characters, of that sense that everybody is on [the collusion].

"Even the kindly old shopkeepers and that sort of thing. They're in on it just by being there.

"In any event, it's given us time to read more, and do more with costumes, locations, the structure of the buildings, houses, types of rooms."