For every Harry Potter Halloween costume you've worn in your life, you probably have Jany Temime to thank.

Those outside the design world might not know her by name, but Temime is one of the biggest costume designers in Hollywood. Originally from France, her resume spans over 40 years. She led the costume design on blockbusters like Gravity (2013), Spectre (2015), and Passengers (2016).

And of course, she's behind the costumes of the last six Potter films: Prisoner of Azkaban to Deathly Hallows Part 2.

Jany Temime

I had the opportunity to chat with Temime while she was promoting her new partnership with Prismacolor, and of course, we had to get into Harry Potter.

As a hardcore Harry Potter fan myself, I'm happy to say I finally got an answer to a pressing question that has circulated in the fandom since 2004: Why did the Hogwarts students suddenly start wearing Muggle clothing in Prisoner of Azkaban?

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If you're not quite as intense about Harry Potter as some (read: me), maybe you didn't notice this costume shift from the first two movies.

But even in the Prisoner of Azkaban scenes when Harry, Ron, and Hermione donned their school uniforms, gone were the Chris Columbus days of perfectly tied neckties under two layers of sweater and robe.

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Instead, the trio and their fellow students attended class with uneven ties, untucked shirts, and a total disregard for sweater etiquette.

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For young Harry Potter nut jobs like me in 2004, this change was nothing short of sacrilegious. Wizards don't dress like Muggles! Some of them don't even know how! And wouldn't students get in trouble if they didn't adhere to the Hogwarts dress code? (As far as I know, there is not actually a Hogwarts dress code mentioned in the books, but still. It's implied.)

But for costume designer Jany Temime and director Alfonso Cuarón, it was a natural development of the characters as they entered their teen years.

Speaking on the decision behind the costume shift, Temime tells me, "[Alfonso and I decided] to make it in a way more glamorous, more cool. Because the teenagers nowadays are extremely fashion-orientated, and in a high school you have to be dressed up."

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It's a good point, and it's one that I'm a lot more on board with now that I've studied film and am no longer 12 years old. Diehard Potter fans may have wanted a carbon copy of the books they had come to love, but Cuarón and Temime are artists — and art is what Cuarón and Temime created.

"The first two Potter films were very Christmas Carol," Temime says, referring to the fantastical design "[Alfonso Cuarón] wanted to have something more realistic."

It was easier for Temime to approach the Potter characters with a fresh eye when she first came on because she was unaware of how massive the Harry Potter phenomenon already was.

"I'm coming from the French cinema," Temime explains. "I believe in a cinema of author. The reason that I did Harry Potter is because of Alfonso. And when I started it, we were making characters, real characters."

Cuarón did not stay on for the next five Potter films, but Temime did. She watched her characters grow before her eyes and adjusted each one's look from film to film accordingly.

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"They evolve," Temime corrects me, when I ask her how she changed the Potter looks over the years. "Ron was always the little one the kids dressed up with the leftover of his hand-me-downs from the brothers. The twins brothers, they became rich and they started dressing better. They don't change, they just evolve."

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But Temime did concede to making a few changes made over the years — specifically she told me about her decision to totally redo the Death Eater's look, from Goblet of Fire to Half-Blood Prince.

"The first Death Eaters that I designed for film are very different," Temime says. "I use that Ku [Klux] Klan hat because it started in the camp site. You could just see the top of the points, that was a very frightening image."

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But, Temime explains, the design that worked well for Goblet of Fire was not very practical for the future films, because it was too hard to fit the tall pointed hats in the frame of the shot.

"It was limiting," Temime admits. "We designed another and then I got the idea of masks ... when we put the mask on then the whole costume was more frightening."

Apparently, the costume team didn't get much help from J.K. Rowling either — no hints at all as to would happen in future books to the characters Temime was designing.

"I remember when I was working number five [Rowling] said to me, 'Dumbledore is gay,'" Temime laughs. "I said, 'You say that now? I designed 20 Dumbledores!'"

Prismacolor

Temime recently partnered with Prismacolor Soft Core Colored Pencils, and she shows me some beautiful sample character designs she sketched out with the Prismacolor pencils. (Which, she assures me, she now swears by, because of the wide variety of colors.)

It's not original sketches, but they're still cool enough to bring out my inner fan girl.

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Thought Potter is now well in Temime's past, she is happy to reminisce with me. But she's also looking toward the future.

Her next film is "Film Stars Don't Die In Liverpool" starring Annette Bening, Jamie Bell, Julie Walters, and Vanessa Redgrave. It's a smaller film based on British actor Peter Turner's memoir, and Temime tells me she was thrilled to work on a low-budget film — something she hasn't done for over 20 years.

And as for her advice to young aspiring costume designers?

"They should really want it, because it's very difficult. But you really have le feu sacré [fire in your belly], if you feel it and think, 'This is the only thing I like in the world. This is my passion.' ... then you manage to make it."