Duffy was cast in 'Legend' on the back of her hit single 'Mercy'.
The 31-year-old Welsh star appears as Reggie Kray's favourite singer, Timi Yuro, in the new movie because of their striking similarities and director Brian Helgeland has revealed how her casting came to fruition.
He said: ''There was a guy who was in 'The Firm' who went to prison with the Krays named Chris Lambrianou and I asked him who Reggie's favourite singer was because I knew music was going to be important.
''He said to me Timi Yuro was his favourite singer. Chris told me how he would book her in all the clubs because he liked her so much.''
The 54-year-old director said having Duffy play the part seemed like a ''fun'' idea.
He told NME: ''I thought that would be a great thread through the movie, to have that live performance from Timi, and I had seen Duffy's video for 'Mercy' - which was very classy, with her up on stage as a nightclub singer.
''So one of the casting directors just got a hold of her. She thought it sounded like a fun thing to do.''
Listen to her new single 'Down'.
Melting Vinyl brought local talent to the fore as it showcased a set by Tokyo Tea Room on the day of their latest EP release, 'Dream Room'.
The Who, Stormzy and more coming this month.
For the Nottingham date of Feeder's Tallulah tour, you just know before it even starts that it's going to be a banging show.
Holy Moly & The Crackers journeyed down from their hometown of Newcastle Upon Tyne to play in Canterbury, where they thought they'd be playing to...
Another exciting month in the world of music.
Listen to Dictator's newest single now.