Blake Lively on Her Body Transformation for ‘The Shallows,’ and Her Obsession with Harry Potter

On Wednesday, Blake Lively sat down with “Extra's” special correspondent Hilaria Baldwin to talk about her new movie “The Shallows” and how her body was transformed for the role. “It was like being an athlete more than an actor,” she said, adding, “It was incredibly physically demanding.”

The actress spent her days batting four-foot waves in the water. “I had to do my own stunts six of the eight weeks, I had to look like someone who was strong enough to be a surfer.” Blake took on her character, Nancy, just months after welcoming daughter James with husband Ryan Reynolds.

“It was eight months after I had a baby. It was such an undertaking, 'cause your body changes so much, not just for vanity's sake, but I had to be strong to keep up with it,” she said. “It was my job to train. No gluten, no soy, and then no processed foods. I had butter, I had sugar, I had all that stuff. It was just making my own stuff. I guess it was close to paleo... it was nice to eat clean like that.”

Blake also opened up about her recent confession that she's a Harry Potter superfan. “I was obsessed with the books… and it was so much fun. The books were coming out so suddenly, but by the time you got to book four, you had John Williams' beautiful score in your head… I'm so upset that there isn't a real place like that.”

She confessed she only recently watched the final two movies because she couldn't reconcile with the fact that there were no more. “At the movies I did all the midnight screenings, I dressed up as Hermione… I broke twigs on my tree and made it look like a wand.” Lively is already geeking out over “Fantastic Beasts,” saying, “It looks amazing!”

Later in the day, Lively confirmed her pregnancy on an appearance of "Late Night with Seth Meyers." Watch!