'It Ends With Us' star Blake Lively on bringing Colleen Hoover book to big screen: 'I've never had such a challenging experience in my career'

Blake Lively said she's "never had such a challenging experience in my career" filming the romance drama It Ends With Us, and for anyone who read Colleen Hoover's best-selling novel, that should come as no surprise. Lively plays beloved lead character Lily Bloom, who overcomes a traumatic childhood only to find herself in a turbulent relationship similar to that of her parents.

"This movie was such a challenge because you have scenes that are deeply painful and traumatic and physical. But you also have scenes that are full of levity, light and romance," Lively, 36, told Yahoo Entertainment. "Having the opportunity to take a character on [who] experiences all of those things is something that I will never take for granted. I've never had such a challenging experience in my career, but that's what's rewarding — getting the challenge of having to go on that emotional journey, having to experience those highs and lows and getting to see that in real time."

Lively, who stars in and is a producer of the film, had no small task when taking on the project. It Ends With Us is huge on BookTok with well over 2 billion views — and counting — on Hoover hashtags. (BookTok is a literature-focused community on the popular social media app.) With that comes a built-in dedicated fanbase and also some controversy. Critics of the book say it romanticizes abuse, while others argue it can be a real depiction of the cycle of domestic violence. The movie addresses it head-on.

"I think for the audience, what's so beautiful is that, like, when Lily is starting to see that there may be cracks in the relationship, she doesn't want to believe it," Lively continued. "Colleen does that so well in her book. And I think that we do that well in the movie where you feel like, Oh, no, no, no, no, no."

Lively stars opposite Justin Baldoni, who plays her troubled love interest, Ryle. Baldoni also bought the film rights to the book and directed the movie.

"Normally when I see this type of character like Ryle onscreen, you know what's gonna happen," Lively said. "And you're like, 'Ah, that guy's full of red flags.' But the way that Colleen wrote Ryle, I think is just so — I think that's why the story resonates with so many is that you get why Lily stays. You get why Lily chooses to believe a different reality because you're watching her in real time. You too are going, like, 'I know what I just saw, but I don't want to, maybe I didn't just see that.' And I think that is the magic of this film — how she made these characters so winning."

Actress Isabela Ferrer, who plays a young Lily Bloom, told Yahoo she felt a "huge responsibility" stepping into a role fans care so much about.

"It was such a huge responsibility of mine to be able to deliver a performance that I felt the fans would want. After reading the book, [Lily's] such a strong and complex character, even from such a young age, that it was just so exciting to be able to play that kind of role, especially as a young actor," she said.

"There's not a lot of complex roles up to that level where you're dealing with so much: you're falling in love, you're in a tough family situation. And to be able to kind of jump into that role was definitely daunting," Ferrer continued. "We had such a supportive team around us, and Alex [Neustaedter] being a co-star was phenomenal. I felt really prepared and ready." (Neustaedter plays young Atlas in the movie, Lily’s childhood love.)

Ferrer said having Hoover's book felt "like an extra script."

"You get to really just dive into a narrative and really take it all in," she added. "It was just such a pleasure to do that."

It Ends With Us is in theaters Aug. 9.