The Irish actor has apparently been cast in a supporting role in Christopher's World War II drama, about the 1940 evacuation of the French city by Allied forces, sources tell TheWrap.com.

This would mark the fifth time the collaborators have worked on a project following The Dark Knight trilogy, the Batman films in which Cillian played the villain Dr. Jonathan Crane, also known as the Scarecrow, between 2005 and 2012. In 2010, they also reunited for psychological thriller Inception.

Dunkirk reportedly features an ensemble cast lead by Kenneth Branagh, Tom Hardy, and Mark Rylance, who recently won the Best Supporting Actor Oscar for another war drama, Bridge of Spies.

Christopher likes to keep his movies top secret, and the rumoured cast have kept tight-lipped about it, with Kenneth's publicist asking reporters at the London Critics' Circle Film Awards in January (16) to not ask about the project, according to WENN.

The director has also been keen to cast relative unknown actors, including Fionn Whitehead, who only has one TV mini-series credit to his name, and U.K. actors Jack Lowden and Aneurin Barnard.

One Direction singer Harry Styles is reportedly making his transition into movies with the film. The speculation has not been confirmed but the pop star, who is currently on hiatus from the band, has been listed as a cast member on the movie's IMDb.com page.

Filming on Dunkirk, which is also written by Christopher, begins in May (16) and will reportedly take place in the real-life locations of the story.

It is set to be released in cinemas in July, 2017.