Emraan Hashmi says upcoming film "Once Upon A Time In Mumbai", in which he plays an underworld don, is a "turning point" in his career and he has worked hard on his physique for the film.

He also says that working with Ajay Devgn in the film was a good experience.

"Working with Ajay was a treat because he is such a great actor. To be in one frame and act with him is intimidating, but you get to learn lots of things, " Emraan told. The film is by Milan Luthria.

Emraan has played characters with negative shades earlier but says "Once Upon A Time..." would be a turning point for him and maintains that it's unlike other dark underworld films.

"It's a turning point of my career. I have played mostly romantic and intense roles. On-screen criminals and underworld dons are mostly one-dimensional but here we have tried to give them an edge, to bring an emotional context... good songs, so that the film becomes more colourful and not dark, " the actor said.

Set primarily in the 1970s Mumbai, the film will trace the changing face of the underworld through the eyes of a police officer. The story follows the rise of Sultan (Ajay), and his eventual fall when his protege Shoaib (Emraan) challenges his supremacy and usurps power to rule the underworld in the city.

The film also features Kangana Ranaut and Prachi Desai.

Asked if there were any particular actor's films he saw to mould his character set in the 1970s, the 31-year-old said: "I think the films I saw were mostly Mr. (Amitabh) Bachchan's and Shashi Kapoor's. I can't name any film in particular."

Emraan has really worked on his body for this film, but says he detests the term "six-pack abs".

"I hate this term six-pack. When Milan narrated the script he made sure that the character demands an overall muscular physique. Because of the action sequences, the toughness in the look was required, " he said.