‘The Notebook’ Costume Designer Took Inspiration from This Glamourous Royal Moment in History (Exclusive)

The Notebook is one of the most classic love stories of our generation.

The movie — which was released 20 years ago today on June 25, 2004 — is based on the Nicholas Sparks novel and tells the story of Allie and Noah, two people who were never meant to fall in love but did, and against all odds, found a life together.

The story takes place over a lifetime, and in the movie, you see two generations play Allie and Noah — and in the flashbacks, portrayed by Rachel McAdams and Ryan Gosling, time (and fashion) starts at 1940.

Costume designer Karyn Wagner pulled together what felt like endless costume pieces for the film to span several decades and that meant creating almost everything from scratch.

“I made about 90% of the costumes because I’m so specific with my storytelling,” she tells PEOPLE while looking back on the film. “I may have rented [Allie’s] swimsuits or bought them vintage, but I like to give the audience visual cues through clothes, and I do that by building everything.”

One of the looks that Wagner created for The Notebook is Allie’s wedding dress — but not for her wedding to Noah. During a break in their romance, Allie found love with Lon (James Marsden), who she planned to marry. The wedding was going to be the biggest event this side of the Mississippi! And that called for a dress to match.

“I wanted to reference the wedding of Princess Grace, because one of the things that costume designers have is what I call a covenant with the audience,” Wagner explains. “There are certain shapes that everybody recognizes. You see that shape and you immediately know where your character is. Grace Kelly is one of those, even if you don’t really know who she is, you’ve seen the photographs of her wedding [to Prince Rainier III of Monaco]. They’re some of the most iconic photographs of weddings ever, and she has this gorgeous, gorgeous dress. I wanted to reference that with Allie’s dress.”

The result was a gorgeous white dress with lace on the bodice and a delicate lace overlay around the neckline. The dress also had long lace sleeves, just like Kelly’s, and a massive veil.

“I wanted to reference, again, the family’s wealth by the amount of lace on the dress and also by how huge the veil was,” Wagner says. “Going back to the sumptuary laws during World War II, you couldn’t have a veil that big unless you were either wearing your great-grandmother’s from Victorian times or you were just wealthy enough to fly it in from France and say, ‘I don’t care what this costs, my daughter’s getting married and she’s going to have an eight-foot veil.’ So that’s a lot of what went into that wedding dress.”

Wagner says the last piece of the puzzle for crafting the dress was that she wanted it to be uncomfortable for McAdams and, in turn, Allie, because it’s while she’s wearing the dress that she discovers Noah is still out there and her feelings for him are still buried deep in her heart.

“I wanted the dress to make her realize that she wasn’t happy about this. Right? She wasn’t happy. She didn’t actually want to be here,” Wagner says.

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Allie and Noah’s wardrobes are worlds apart — because their characters come from different walks of life in their early years. Noah lives with his single father who is working class, while Allie comes from a wealthy two-parent home.

Wagner painted that picture with their clothes, including with Noah’s simple shirts and pants, that she says she imagined he purchased from a Sears catalog or the general store. She says he likely would have only bought one or two new shirts a year, and only if he absolutely needed to, whereas with Allie, her mother would have taken her to the big city to a modiste for custom-made clothing in far excess of what she actually needed.

And even though Noah’s clothes were on the simple side, Wagner says she still custom-made each piece — down to the T-shirts he wore (in multiples, just in case something snagged while he was renovating the house).

But you can’t talk about The Notebook costumes and not talk about the blue dress. You know the one. It’s the simple short-sleeve dress that Allie wears when she comes back to Noah (and actually wears for a good portion of the film) after several years away. It’s the dress she’s wearing when she realizes that maybe their love story isn’t over.

And it’s the dress that Wagner knows is part of her legacy as a costume designer, no matter how many other projects she works on during her career.

“It makes me feel so great as a costume designer that the blue dress has become so iconic,” she says. “Clearly I hit some nerves.”

The inspiration for the dress started with the British painter J. M. W. Turner. Wagner saw one of his paintings that she said melded the blue of the Thames in England and the greenery surrounding it and those colors created what she wanted for Allie’s dress and the scene around it.

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“Part of it was that when [Allie and Noah] have this great moment and she has this epiphany that this is what she wants and she doesn’t care how poor she’s going to be, and she doesn’t care how uncomfortable it’s going to be, I wanted her to be one with her environment, hence that blue, because the skies in Wilmington were like that blue,” she says of the scene in the movie and their filming location in North Carolina.

But Wagner wanted the dress to be both sophisticated and simple — a combination of where she came from and where she was inevitably going. And the blue also symbolized her hopefulness for the future.

“I kept the adornment very simple, because I wanted [Noah] to be able to see past the dress,” she says. “I wanted Noah to be able to incorporate the dress in his psyche, but still see her. So the dress had to be there, but not there. It had to be hopeful. It had to be a little bit more simple than anything else, a little less sophisticated, a little bit of a throwback to when they fell in love.”

She also admits, quite simply, that the dress just looked good on McAdams, which is the ultimate goal for a costume designer.

“I always forget to say these things because it seems so obvious, but it’s a really beautiful color on Rachel,” she says. “It really highlighted the blonde in her hair, and it was great on her complexion and suited her figure. It really makes me happy that I did something right with this dress.”