Dakota Johnson has admitted she felt a level of “pressure” starring in the film adaptation of Colleen Hoover’s Verity.

The psychological romantic thriller novel, released in 2018, has sold more than one million copies.

However, after she uncovers what appears to be Verity’s chilling autobiographical notes, she wrestles with the disturbing and twisted confessions about Verity’s husband Jeremy (Josh Hartnett), and wrestles with separating fact from fiction.

Speaking at the film’s London premiere, Johnson told the Press Association she felt the weight of delivering an adaptation that fans of the book would be satisfied with.

“I always feel like any book adaptation is tough because every person reading a book, the experience is so insular,” she said.

“So, it’s very much your own imagination that you are really glued to.

“But I think people will be excited.

“Annie does an incredible job in this movie.

“There’s pressure, but also like, what are you going to do?”

Her co-star Hartnett echoed the sentiment.

He said: “I absolutely feel the pressure.

“But at the same time, you want it to feel fresh.

“I’ve done a couple of book adaptations, and if you are trying to stick to the letter of the book, it’s going to come across stale because you can only get so much of the book in there and so you can’t get all the nuances of the book.

“So in order to do that, sometimes you have to take the essence of what’s meant to be in that particular scene and/or that series of scenes and kind of condense it down to something that makes more sense cinematically, and I think (director) Michael (Showalter) did an excellent job of kind of doing that with this book.

“In that same way, I think the people who’ve read the book and loved the book will also be surprised that they’ll really enjoy the process.”

The original novel ends with a huge, ambiguous twist that leaves readers guessing what actually happened.

Hartnett said he was looking forward to seeing how viewers reacted to how the film tackles the shocking ending – and wants them to leave the cinema debating their theories.

He said: “That’s what I want.

“Everybody keeps asking me, are you team manuscript of letter and I’m like ‘I’m not going to say’, because I want people to debate and come up with their own idea of what they think and who they believe.

“And if they do that and they come out and have a fight about something, that’s this kind of fun and you know it’s an intriguing and dark film.

“You don’t get to see it very often in film, like especially in big films, you don’t see ambiguous endings very often.”

The director said: “I spoke to her all the time, and when we were in the prep portion of the movie before we were shooting and still working on the script, I was constantly asking her questions by text, like ‘What did you mean by this? What did you mean by that’, and then she sent me her original manuscript.

“She sent me the Word document that she wrote the book on, so that I could easily search through it and find things.

“And she was a very close collaborator on this project, especially around those kinds of things, and then she was on set on multiple occasions.

“Then in post-production, she came and watched cuts of the movie, gave notes, gave her opinion, gave ideas.

“It was very important to me that she liked the movie, because at the end of the day, it really is about her fans of her book.”

Showalter added: “So I’m very grateful for the fact that we had Colleen as a constant resource throughout the whole project.”

Speaking of the three main stars, he called them “hardworking professionals who take their work very seriously”.

He said: “But I love them dearly as human beings, and I’m just big fans of theirs.

“Getting to work with these actors and see them working together and the way their performances blend so nicely in this film, it was important that we have this kind of cast.

“It’s like these three jewels in a crown.”

Verity is released in cinemas on October 2.