Adapting a beloved book into a film or TV show is not easy, but Blake Lively and author Colleen Hoover promise that the onscreen version of It Ends With Us will be satisfying.

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"Some people will always like a book better than a movie and some people like a movie better than the book, but I think that we just did our best to honor the book and honor the fans, and, I think, really make something that works even by itself," Lively told ET Online. "If you don't know the book, the movie works. I don't think there's any way that if you read the book and you saw the movie that you wouldn't be thrilled. We really worked hard on that. I also believe if you saw the movie and then read the book, you wouldn't go, 'Hold on, this isn't like [the other].' You can do either. I think they're both really beautiful."

The author agreed with Lively, adding, "Readers tend to always want to read the book first. I completely understand that, but I feel like this adaptation has stayed so true to the book that it's actually either or, whatever you prefer. I think that you'll be happy if you watch the movie and then go into the book or vice versa."

It Ends With Us stars Lively and Justin Baldoni in the devastating romantic drama based on Hoover's parents' relationship. The story centers on Lily (Lively), a woman who overcomes a traumatic childhood with an abusive father to begin a new life in Boston. Things seem to be on track as she follows her dreams to open her own flower shop business, but when she falls in love with charming neurosurgeon Ryle (Baldoni), she begins to realize his abusive behavior only continues the harmful cycle she's been trying to escape her whole life.

"This is the book that means the most with me," Hoover said. "I've tried to have other books adapted and it didn't quite go to fruition. I've been praying this would happen for four or five years now, so it just means so much to me. This book is the one that's personal to me, so to get to see it on screen [is meaningful]. I watched it for the first time with my mother, who inspired the story, so words can't express how amazing this whole experience is."

Lively is "so proud" of how they were able to bring It Ends With Us to life onscreen.

"I'm just so proud of this film," she added. "I'm just so proud to be here and sharing it with Colleen and the fans. It's just really special. It was a great honor to take on Lily... This story resonated with so many people, so there's a great responsibility that comes with that. You want to honor this book and this character that people love so much, but you also want to bring a life and a humanity to it that is true to who you are. It's a lot of different things that you want to accomplish in this story."

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Since Hoover has "such a dedicated fan base," Lively knows that connecting with those who have read the book is the "most important part" of the movie.

"[Hoover was] self-published initially, so this is somebody who the fans really authored the success of your stories," Lively said. "She wrote stories that resonated with people and didn't go to all the traditional means that people go to. She went directly to the people she was speaking to and they came forward in masses."

It Ends With Us arrives in theaters Aug. 9