Begin Again director John Carney has said Adam Levine was the perfect casting for the film because he could bring his inside knowledge about rock star quirks.
John, who also directed Once, helmed the film about an aspiring singer in New York (Keira Knightley) who is dumped by her boyfriend (Adam) after he finds fame, and she befriends a disgraced music executive (Mark Ruffalo).
The director said of how much Maroon 5 singer Adam is like his character: "Adam is quite different from this character, but he brought to it an awful lot of his own experience of being in the music industry.
"We used to have a thing where he would ask me, 'Hey John, what level of douche am I at today, am I a douche six or a douche seven?'
"I was like, 'You're douche five, you will be douche seven tomorrow when you break up with her,' which was kind of fun."
But John continued of Adam's character Dave, who becomes more and more egotistical as he gets more successful: "I don't see the character as just a douche bag or an a**hole, he does some bad things in the film, but I see him as a young guy who for him, fame tests.
"He's a guy in New York, a kid basically, who's got this break and he tests it and that's what happens when you become famous or rich. The fame fairies send you these little speed bumps and you're tested along the way."
He added: "Adam did a great job of bringing bits of his life into my movie and making it real and filling out a few gaps that I had left, not being a rock star myself, that he steered me right on and brought to the character."
However, John said the rock star vibe hadn't rubbed off on everyone as he had asked James Corden to write a terrible song for one scene and explained: "He was like, 'I'll play you this thing but it's actually quite good, I don't know if it's going to be bad enough,' and I was like, 'Trust me, that's s***'."
Begin Again is in cinemas now.