She may don her Daisy Dukes and bikini tops with pride, but Katy Perry still struggles with her self-image – and that's when she turns to her fiancé, comedian Russell Brand.

"I think he taught me a lot about inner beauty and confidence in myself," the singer, 25, tells Seventeen magazine in its September issue.

"I don't really feel pretty ever," she says. "Without makeup, I feel ugly. And so I would have to sleep with makeup on, or feel ugly and gross. He looks beyond all of that, which is such a win, because I've never felt that with anybody."

The couple may have their differences ("He's a very spiritual person, and I'm constantly struggling with the idea of being spiritual and material"), but Perry says their love is the real deal.

"He's in love with the person inside of me," she says, "and the outside of me is just a bonus."

And as the couple prepares to tie the knot, Perry stills remembers her initial attraction to Brand.

"He changed my mind about him the moment I met him," she says. "I said, 'You are a better person than how you are portrayed.'"