Danica McKellar is revealing a, well, revealing new side to herself.

The former "Wonder Years" star, 38, revealed her killer abs while on the set of Avril Lavigne's new music video yesterday.

"Just had the best time shooting @AvrilLavigne's new video," she tweeted. "And she is so sweet and fun! Made me feel like a rock star. ;)"

Danica McKellar Returns to Acting

(The feeling was mutual. Lavigne, who recently married Nickelback frontman Chad Kroeger, tweeted "Thank you @danicamckellar for acting in my video. You are beautiful and so sweet. We kicked butt! #ROCKNROLL")

Photo: Avril Lavigne's Black Wedding Dress

McKellar, an author who writes math books for children, has been very outspoken about attachment parenting and recently revealed that she breastfed her son Draco until he was 2.5 years old.

"You can breastfeed as long as it works for both you and your child, you know?" she told ABC News in May. "For me it was two and a half and for you it might be three and a half or three months or whatever it is that works."

(Photo credit: AKM-GSI)