Sienna Miller's role was cut from the upcoming film "Black Mass," starring Johnny Depp weeks before its release in order to narrow the scope of the story, said director Scott Cooper.

"It came down to narrative choices," said Cooper, according to The Boston Globe. The reason behind the decision was to shift the focus to Johnny Depp's character, Whitey Bulger, and his life before he left Boston, and that the Irish gangster's years as a fugitive with Miller's character were "less dramatic."

Miller played the role of Catherine Greig, Bulger's girlfriend who lived with him throughout his 16 years as a fugitive and received an eight-year prison sentence for helping the notorious gangster evade capture, according to Entertainment Weekly.

"She was quite a character from South Boston. The accent was something I really focused on because playing someone from Southie, you don't want to mess that up," she said. "Hopefully I've managed to pull that off, although I think everyone's like, 'How can you be English and think you can do that?'" Miller said about her character in an interview last year.

In the interview, Miller also spoke about how small her role was in comparison to the rest of the film's cast.

"I shot for two weeks, it's a really cameo," she said. "It's not a leading role. I had an amazing time working with Johnny Depp, who I think is extraordinary and Scott Cooper, the director, who's made some amazing films as well. The story's in the right hands and it was amazingly fun to come in. I got to be from Southie, I got to age from 28 to 56."

"Black Mass" is packed with a star-studded cast and also stars Benedict Cumberbatch, Joel Edgerton, Kevin Bacon, Dakota Johnson, Corey Stoll, Adam Scott and Peter Sarsgaard. The film follows the story of "one of the most notorious criminals in U.S. history" and is slated to hit theaters on Sept. 18, The Wrap reported.