Natalie Portman Talks Jackie Kennedy's Strength In The Face Of Tragedy After Playing Her 

After portraying Jacqueline Bouvier Kennedy for the increasingly acclaimed film

, Natalie Portman reveals that she came away admiring the former first lady for the strength she displayed throughout her life.

“I loved that she defined herself as a wife primarily, but then lived a life that was very counter to that, where she was her own woman so strongly,” Portman told PEOPLE at the Hollywood premiere of the film Monday at the American Film Institute’s AFI Fest 2016. The Oscar-winning actress, 35, portrays the grieving, traumatized first lady as she searches for the inner strength to move forward in the days following the assassination of her husband, President John F. Kennedy, in November of 1963.

“It was like she didn’t know how to be any other way, except exactly herself and very, very strong,” said Portman. “Very able to author your own story, and she really became the author of her own story – and his story.”

Portman was also impressed by how Jackie Kennedy was able to open herself to sharing her mourning with the grief-stricken American people through an elaborate, poignant and very public funeral service for her husband.

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“I think she obviously was much more public than I’ve ever been,” the actress said, “but as a public and a private person, the understanding she had that even when she was going through something incredibly private, it meant something to other people how she presented herself publicly. And that isn’t just like, ‘I’m having a hard time; stay away from me; leave me alone.’ It’s like other people share in whatever you’re going through, and that’s really, really impressive that she was able to do that.”

Portman, who is pregnant with her second child with husband Benjamin Millepied, said she found her way into her performance first by studying the minutia of Jackie Kennedy’s physical mannerisms and way of speaking before developing her deeper take on the first lady, who went on to become a prominent socialite and book editor before her death at age 64 in 1994.

“I think the easier things were — even though it was challenging, also — just the more superficial details, like the way she talked and the way she moved and the way she looked,” said Portman. “Those are things that you spend a lot of time on, but it’s really the way she felt that takes the imagination and the real searching. The other stuff is more like learning a skill, as opposed to exploring your own depths.”

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