*Jordin Sparks says she had to constantly talk herself into believing that she deserved her starring role in “Sparkle,” and that she had the acting chops to pull it off.

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“I had to believe in myself and say, ‘They picked me, they put me here, they cast me for this. I know I have what it takes to do this’,” the “American Idol” winner told AOL Music.

The 22-year-old credits her cast mates, including the late legend Whitney Houston, for helping her portray the film’s lead character and namesake, Sparkle. “The cast was so amazing, helping me with open arms,” she said. “They didn’t have to do that, and I wasn’t expecting it. I thought it would be more like a hazing thing! I had nightmares of stuff like that happening.”

As Jordin recounts, Houston spent her last months before her tragic death this past February as a mentor on set. “She was wonderful,” Sparks said. “She wore the executive producer hat, and she wore the coworker hat and the actress hat. And then right after a scene, she’d be right there saying, ‘Do you need anything? How did you feel about that?’ Sometimes she would be there telling me it was OK after a really emotional scene, after I’ve dug deep to a place that I don’t really want to think about. The director would yell ‘cut,’ and sometimes, I couldn’t stop crying. And she’d be right there rubbing my back saying, ‘It’s OK, it’s OK, I know.’ She was amazing.”

Sparks said that her musical tribute to Houston at the 2012 Billboard Music Awards “was the scariest moment of my life, so far. That was the first time that I had ever performed that song [‘I Will Always Love You’]. It was one of those things where you look through Whitney’s songbook and say, ‘I’m going to leave ‘I Will Always Love You’ in a pretty wrapped box on a pedestal, and I’m going to go over here and sing ‘I Wanna Dance With Somebody,’ ’cause nobody is going to get mad at me for singing that!’ So, my knees were shaking, my hands were clammy, my heart was pounding. I was sweating, dry throat, everything. Every nervous tick you could have, all at once. I don’t even remember what happened. I was up there, and then I was not! All of a sudden, I was backstage again.”

“But it was one of those moments where I definitely felt her presence,” Sparks added. “She was all around that arena, and I just knew from spending time with her on set, she was like, ‘You got this. You go, girl. You got this.’ That’s how she was. She wanted to see everyone else shine, which is incredible, because there aren’t a lot of people who are like that. Especially people who are more established, they don’t want anyone coming to take their spot!”

“Sparkle” arrives in theaters Aug. 17.