Aaron Eckhart - Eckhart Challenges Co-star Ne-yo's Battle: Los Angeles Set Account

The R&B star-turned-actor told Etonline.com that he fell out with his method acting co-star because he couldn't understand why Eckhart stayed in character after the cameras stopped rolling.

The So Sick hitmaker plays one of The Dark Knight star's soldiers in the film, and admits he struggled with the project at times as Eckhart insisted on continuing his onscreen persona even when they weren't working.

But Eckhart insists the singer/songwriter's account is wrong - and the camaraderie of the cast was always evident.

He says, "We ate, drank, slept, showered, everything together... By the time we were actually filming, we were a tight group; we knew each other, what favourite song, where we were from."

But the actor accepts there were moments when he was advised to stay in character as a staff sergeant.

Eckhart adds, "We engendered that on set... There's a lot of stuff going on.

"This is an alien movie but, to me, it was, 'This is my war movie'... I was 'staff sergeant'."