Simon Cowell's Discoveries

Ever since she was a kid singing into a hairbrush and putting on performances for her parents, Leona says she's dreamed of being where she is now.

And she says being compared to Mariah and Whitney is amazing. "It's a big compliment," she says. "They've had such long, successful careers. ... I can only hope to one day follow in their footsteps."

Simon says Leona truly blossomed over a few episodes of The X Factor. "On the third show, something changed," he says. "Overnight, I could see her transform from a great singer into a superstar. And she's one of the nicest people I have met in this business."