Sarah Michelle Gellar Steals the Show Wearing Backless Dress and Spanx

Sarah Michelle Gellar looked like the star she is at the CW, CBS and Showtime's Summer TCA Party in L.A. on Monday.

She wore a backless Izmaylova dress with peplum detail. The star glowed while posing for photographers at the star-studded event.

What the photos did not show was what the 36-year-old actress was wearing underneath her dazzling black dress.

"Yes, I'm wearing Spanx," Gellar admitted to Us Weekly. "And I've been wearing Spanx all day. God bless the woman that invented them!"

The mother of two- her children are daughter, Charlotte,3, and Rocky, 10 months, with husband Freddie Prinze Jr., 37-said that she is in good shape because she has been "chasing two children all day long." As Gellar explained, "I take advantage of being in California: 'Let's go outside! Let's do this!'"

Gellar will star in a new comedy series called The Crazy Ones. She will play a level-headed advertising executive who works for her wacky father's (Robin Williams) company. "Being able to have Robin sort of take the lead, for me it's the best of both worlds," said the star, who previously played twins on The CW's Ringer. "I get to spend time with my family and I get to do a job that I love."

The Buffy the Vampire Slayer star said that working with Williams has been a dream come true. "He understands the dilemma that I find being caught between my home life and my professional life. He couldn't be more caring," Gellar said of Williams, 62.

"My joke is that I actually didn't apply to be on the show -- I actually applied for Robin to adopt me. I didn't realize it was actually a job on a TV show, but since that was second best, I took it!"

The Crazy Ones premieres Thursday, Sept. 26, at 9 p.m. EST on CBS.