What did Jackie really know? Get new details about her complicated marriage to JFK, her suicidal despair after his death, and how she found the strength to go on. Subscribe now to get instant access to this Kennedy confidential, only in PEOPLE.

While Natalie Portman has made many memorable physical transformations throughout her 20-year acting career (see: Black Swan, V for Vendetta), the preparation for playing real-life icon Jackie Kennedy in the upcoming movie Jackie carried a lot more weight.

Because the film takes place around the 1963 assassination of JFK, Portman, 35, and the filmmakers had to capture a specific place and time in Jackie’s life, look and mental state. Here are the five ways Portman transformed for the role, a performance for which she’s already considered a strong contender for another Best Actress Oscar nomination.

1. The voice

“Her voice and her accent and her movements are very, very specific,” says Portman, who studied Jackie’s 1962 televised tour of the White House and a series of interviews with historian Arthur Schlesinger conducted in 1964 to help her master Jackie’s speech and movement. “I was reading everything I could find and then I was working with a great dialect coach, Tanya Blumstein,” the actress recalls. “We just listened and watched the White House tour specifically, but also some of her audio tapes of her interviews, over and over and over again. I was really learning exactly the way she said it, with the pauses in the same places and the breaths in the same places and the hesitations and all of that.”

2. The eyebrows

Makeup artist Miwoo Kim tells PEOPLE she focused on Jackie’s eyebrows first.

“She always had perfect eyebrows,” says Kim. “What truly makes Jackie’s facial features are definitely her unique and strong eyebrows. On Natalie I used a technique to make her eyebrows thicker, set wide apart and in a square shape.”

As for the rest of Portman’s makeup, Kim says she focused on recreating Jackie’s elegant look. “She had a beautiful, natural skin tone,” says Kim. “She often used pink lipstick — the color changed according to the dress she chose to wear.”

F:PHOTOMediaFactory ActionsRequests DropBox46786#Fox138_J_00204_A.jpg
Credit: Stephanie Branchu

3. The hair

Portman admits that Jackie’s iconic bouffant hairstyle was a key component to her performance — along with the makeup and clothing. “I looked in the mirror and I have this iconic bouffant and the eye makeup with the little wing and the classic Jackie suit. You feel like a different person,” she says.

A bonus fact about Jackie’s original ‘do: Her signature bouffant was created by celebrity hairdresser Kenneth Batelle, who also styled Marilyn Monroe.

Credit: Cecil Stoughton/The LIFE Images Collection/Getty; Bruno Calvo

4. The clothes

Portman considers Jackie’s memorable and frequently photographed suits and pillbox hats an emotional cornerstone to the film.

“[The film] takes place around the assassination, so they carry a lot of emotion within them,” she says. “The pink suit with JFK’s brains on it that she chose to keep on after the fact, because she was already aware that it would be symbolic for people, that she was a living testimony to the events of what happened. Even though it was probably extraordinarily traumatic to have on, the clothes have a symbolic meaning to how quickly she was able to be aware of what it meant for the country at the same time as what she was going through privately.”

Credit: AP; William Gray

5. The emotions

“The assassination scene was definitely the hardest,” Portman says of getting into Jackie’s emotionally distraught headspace following the death of her husband. “I think it’s just something that no one has ever experienced it except for her, and how horrible for her.”

The actress admits she found the experience harrowing — both acting in the assassination scene and watching the real-life version over and over. “I was dreading it, it’s just awful when you’re very connected to a character and then that’s clearly the worst day of their life and you have to be in a place mentally where you’re not expecting it before it happens. It was definitely a scary one.”

  • Reporting by MARY GREEN