The ballroom belonged to the grown-ups on the Season 12 premiere of "Dancing With the Stars" with Kirstie Alley and original "Karate Kid" Ralph Macchio stunning the crowd (and judges!) with the best performances of the night.

Alley, 60, also unveiled something fans haven't seen in a while: her long legs!

The show's Emmy-winning costume designer, Randall Christensen, reveals the decision for the former "Cheers" star to bare her legs, which have been toned by her ballroom lessons, was a collaborative one. "We both agreed that her skirt had to be shortened. Kirstie's legs are looking fantastic and this few inches above the knee made all the difference in the world," he says.

dancing with the stars costumes

Kirstie Alley and Maksim Chmerkovskiy, Kendra Wilkinson and Louis Van Amstel. Photos by Adam Larkey, ABC

It was Alley's partner, sexy Ukrainian Maksim Chmerkovskiy, who asked for the hem of her shimmering, black cocktail-length dress, to be dropped seven inches in the back to give the frock flirty movement for her cheeky cha-cha-cha.

"It was a good call. Kirstie showed me some of her dance moves. The opening sequence when she shakes her booty was only enhanced by the new cut of her skirt," Christensen says.

Was Alley happy with the look? "I feel like Cinderella tonight," she tweeted.

The designer, who spoke to StyleList exclusively after opening night, also gave us some behind-the-seams dish on some other celebrities' bedazzled looks:

dancing with the stars costumes

Ralph Macchio and Karina Smirnoff. Photo by Adam Larkey, ABC

Macchio: The 49-year-old actor may have permanently changed his "young grasshopper" image with the "Rat Pack" inspired velvet dinner jacket Christensen's team created for his debut foxtrot with partner Karina Smirnoff. The duo, who topped the leader board, have dubbed themselves "Team Kamacchio." Smirnoff's dreamy, peach two-piece ensemble was a sexy nod to the "Mad Men" look.

Kendra Wilkinson: After pledging not to show too much skin on the reality dance floor, the former Playboy centerfold wore a revealing, pale-blue minidress with a flirty, fringed hem and barely there back. "Kendra is so petite it could be easy for a big dress to overwhelm her. I wanted to emphasize her great physique as well as her voluptuous curves," explains Christensen. Her partner, Louis van Amstel, requested the three individually placed, handmade crystal strands that ran along the exposed back of the dress. The jeweled pieces moved through the air, refracting light as the reality star danced.

Petra Nemcova: The supermodel, who went to design school, had a hand in creating her pale-lavender gown, to perform a foxtrot the tsunami survivor dedicated to the victims of the recent Japan earthquake and tsunami. "Petra is so elegant and statuesque it seemed like the perfect costume to reflect who she really is," says Christensen.

Meanwhile, read what Christensen had to say about his plans for dressing the rest of the cast this season.

And here's the scoop on Nemcova's recent engagement.