Anne Hathaway steps out for 'The Idea of You' premiere, shares how film was a birthday gift for herself

Anne Hathway was all smiles as she walked the purple carpet for the premiere of "The Idea of You" in New York City on Monday night.

The actress, who stars in the film alongside Nicholas Galitzine, dazzled in a red gown with cutouts and paired the look with diamond earrings.

She also posed on the carpet with Galitzine, producer Gabrielle Union, and fellow stars Reid Scott and Ella Rubin.

"The Idea of You," which is based on the book by Robinne Lee and directed by Michael Showalter, follows Hathaway’s character, Soléne, a 40-year-old single mom recently out of a marriage, who attends Coachella, where, in a chance encounter, meets 24-year-old Hayes Campbell, played by Galitzine, the leader of the boy band August Moon.

Hayes is instantly smitten with Soléne and dedicates a song to her while performing at the music festival.

When Soléne returns to her normal life -- working at an art gallery and being a mom to her teenage daughter -- Hayes finds her and the two begin a romance, but face scrutiny by the media.

While speaking to "Good Morning America" at the premiere, Hathaway, who is also a producer on the film, said she was "honored to be asked" to play Soléne and praised Union and producer Cathy Schulman.

"I read it and I love love stories," she said. "I’ve been really lucky to be in a lot of them. I’ve been in a lot of mixed-tone films as well. And so, to find a love story at this stage of my career that rang as true, I just wanted to sign up immediately."

"Also, I just thought Cathy Schulman and I were talking about it and I said, 'I really want this to be my 40th birthday gift to myself,'" she added. "So, I can’t think of a better way to turn 40 and I actually turned 40 the day before we shot Soléne’s 40th birthday."

Galitzine also talked about what it was like acting alongside Hathaway.

"We literally spent every single day with each other for about two months," he said. "It was usually laughter, or crying scenes and I just feel like I’ve learned an incredible amount from her as well."

"The Idea of You" streams globally on Prime Video beginning on May 2.

ABC News' Will Linendoll and Rebecca Anderson contributed to this report.