Jennifer opens up and says she thinks she stinks at singing. 

Jennifer, who will be on the cover of the new issue of Cosmopolitan magazine, admits that for a while, she didn't feel confident in her vocal ability.  Funny, isn't she a judge on a show that has to do with singing?   "The biggest insecurity I had was my singing," she tells the magazine. "Even though I had sold 70 million records, there was this feeling like, 'I'm not good at this.'" 

What helped her get over those fears, she says, was advice from her ex-husband, Marc Anthony.

"He kept telling me, ‘You're the only one holding yourself back from reaching your full potential as a singer. You have to let go,'" she recalls. "I was always so insecure and just kind of going along. Then I grew, little by little, and realized, wait a minute, this is not a fluke. I'm not a mistake – I work my ass off. And I know what I'm doing."