Long before she became the reigning pinup queen for lad mags like Maxim and FHM, Megan Fox made her film debut opposite Mary-Kate and Ashley Olsen as a spoiled teenage heiress in the twins’ 2001 romp “Holiday in the Sun.” She was 15.

“I wanted to act since I was a toddler, and I was just so happy to get out of school,” she recalls of the Bahamas-based shoot. As for any savvy career advice from the seasoned child stars, “there was none,” she says. “We were all so young. But watching them, I saw how terrified they were of the crowds of fans, and I never understood it.” Today, she does. “There’s definitely a price — you can’t go anywhere without people staring, you can’t eat without people taking pictures, and you become introverted,” she notes. “It’s nothing like what they go through, but I do feel like I’m in petting zoo sometimes.”

The Tennessee native, an avid dancer since she was 5, went on to star opposite Lindsay Lohan in “Confessions of a Teenage Drama Queen.” “I’d just left high school, and I was so green,” Fox recalls. Again, there was little in the way of help or inspiration. “We weren’t the best of friends,” she admits bluntly. “But 16- and 17-year-old girls generally don’t get along with each other.”

Now Fox, whose credits include ABC’s popular comedy series “Hope and Faith,” seems poised to outstrip her former child co-stars, thanks in large part to her breakout role opposite Shia LaBeouf in “Transformers.”

The in-demand actress returns for the sequel, “which picks up two years later,” she says. “I’ve read the script like 18 times, but I honestly don’t understand it.”

And she landed the lead role in the Diablo Cody-penned supernatural thriller “Jennifer’s Body.” “It’s a very dark, sexy, inapproriate comedy, and the first time I’ve ever been excited about the work I’ve done and haven’t been horrified by the choices I made,” she says.

Recent breakthrough: The former child star had all the boys drooling with a shallow role in “Transformers.” Now she gets her revenge in Diablo Cody’s “Jennifer’s Body.”

Role model: “My mom. She has an amazing attitude and energy.”

Next: “How to Lose Friends and Alienate People” opens today. Fox plays “a very manipulative, very dumb actress called Sophie. She’s basically a stereotype of a Hollywood starlet — and so much fun to play.”