The actress is in awe of the esteemed actors she rubbed elbows with while shooting her upcoming film, The Butler

Credit: Pacific Coast News

It’s intimidating enough to play Jackie O, but Minka Kelly felt even more pressure to perform when she found out who was joining the cast of her latest film, The Butler.

“I’m not worthy. I feel so lucky and grateful. I was like, ‘What am I doing here?!’ ” Kelly tells PEOPLE of starring alongside Robin Williams, Forest Whitaker, John Cusack, Vanessa Redgrave, Jane Fonda and more in the upcoming film, which tells the story of a butler who served eight presidents.

The movie also features another major star: the one and only Oprah Winfrey. “I didn’t get to meet Oprah because our shooting schedules were different, but she’s a pretty loved lady,” Kelly says. “I have yet to hear a bad thing about her!”

Kelly found that the most difficult part of playing Jackie Kennedy was nailing the former first lady’s distinct accent. “I think she spoke in a way she thought she should speak, so getting that down was hard. There’s a musicality and rhythm to the way she speaks,” Kelly explains. “I went to sleep listening to her.”

Another tough task? Slipping into the retro costumes. “My body is so different from her because I have curves, so fitting into those vintage clothes was actually really hard,” she shares. “Also it was hot – and there was a lot of wool!”

But Kelly had no issue slipping into the stunning Oscar de la Renta gown (left) she strutted down the runway in at the Red Dress Collection fashion show in N.Y.C. on Wednesday night. The actress walked for the second year in a row in honor of The Heart Truth campaign, which encourages women to monitor their heart health.

For the month of February, Diet Coke will donate $1 for every person who uploads a heart-inspired photo to Twitter or Instagram using the hashtag #showyourheart. Visit to for more information.