Credit: Eric Charbonneau/WireImage

Who knew Blake Lively was such a bad girl?

When the 23-year-old actress teamed up with Ryan Reynolds to film Green Lantern last year, Lively says she often tempted her costar into cheating on his diet.

"I would cook for the entire crew and I would try to lure him into eating some of the treats," she told Us Weekly at the film's L.A. premiere Wednesday. "Cupcake lollipops, fresh candies, homemade caramel and marshmallows covered in chocolate -- stuff like that."

Her main objective? "I was trying to sabotage him," she joked of the ripped leading man. "I am a horrible person!"

Lively -- who recently began dating Leonardo DiCaprio -- added that she wouldn't put it past Reynolds, 34, to return the favor if she returns as Star Sapphire in a Green Lantern sequel.

"He is going to sabotage me! He is going to spike my drink with cupcakes," she laughed. "No, luckily his suit was CGI, so maybe they can CGI my suit and get me a 12-pack. That would be nice!"