Ariana Grande, star of the new Nickelodeon show Sam & Cat appears on the August 2013 cover of Seventeen. Credit: Ben Watts for Seventeen

A nasty costar made Ariana Grande feel insecure during the beginning of her career, the actress reveals in the August issue of Seventeen. After starring in a series of stage musicals, from 2010 to 2013, the 19-year-old Boca Raton, Fla., native played Cat Valentine on the tween show Victorious alongside Victoria Justice, Avan Jogia and Leon Thomas III.

Though Grande doesn't refer to her tormentor by name, she does admit that her confidence faltered. "I worked with someone who told me they'd never like me. But for some reason, I just felt like I needed her approval," Grande explains. "So I started changing myself to please her. It made me stop being social and friendly. I was so unhappy."

UPDATE: Though some speculated Grande was talking about some of her Victorious costars, she issued a statement clarifying her comments to Seventeen: "My years filming Victorious were some of the happiest of my life and that cast is family to me. The stories I shared with Seventeen were actually reflective of a different work experience. Please don't send hate to anyone, it's undeserved and I would never want that. Love you guys very much, and thank you for being here and supporting me. Also, thank you to Seventeen for allowing me this opportunity."

Since Victorious wrapped production in February, Grande is now starring in her own Nickelodeon series, Sam & Cat. The comedy also features 20-year-old Jennette McCurdy (iCarly, Lincoln Heights) and 71-year-old Maree Cheatham (Days of Our Lives, General Hospital). Grande is also recording new music. Tentatively slated for an August release, "The Way" singer's forthcoming album Daydreamin' has been in the works for three years.

"I'm a big perfectionist!" Grande tells Seventeen. "I'm trying to channel super-confident women like Alicia Keys, Mariah Carey and Beyonce, because I realized that if you want something, you really have to go for it, just like they do."

The August issue of Seventeen is on newsstands July 2.