Singer KIMBERLEY LOCKE is headed back to "American Idol" Wednesday for a special guest performance, so naturally she needs a fabulous frock. Can "Project Runway" winner CHRISTIAN SIRIANO whip up something "fierce" and "ferosh" for her in the nick of time? Duhhhh!

"Kimberley's faaaa-bulous," the 22-year-old designer says. "She's, like, the most amazing client any designer would ever want. She has opinions but they're good opinions, they're not like 'Judgy was a bear' opinions." (His actual words!)

"I said just, 'Do you, be you,'" she explains. "I don't want to stymie his creative process."

She says "it feels good to be invited back" to the "Idol" stage and that she's a big fan of CHIKEZIE this season: "I think he is the one to watch. He is very diverse and not afraid to cross the genre lines."

After she sings her new single, "Fall," she's agreed to auction off Christian's gown with the help of "Clothes Off Our Back" to benefit her charity, Camp Heartland.

As for Christian, he'll be a judge for the upcoming Miss USA pageant on April 11, and says he's been designing pieces for HEIDI KLUM and his new "Runway" BFF, VICTORIA BECKHAM.

"Her birthday's coming up in April, so you never know, you might see my dress on her. We'll see!"