The actress tackled the role of President John F. Kennedy's wife for Lee Daniels' new film, and admits it was a challenge to master the fashion icon's distinct accent.
She tells People.com, "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. I went to sleep listening to her."
Kelly also struggled with Kennedy's retro outfits, adding, "My body is so different from her because I have curves, so fitting into those vintage clothes was actually really hard. Also it was hot - and there was a lot of wool!"
The movie chronicles the life and career of Eugene Allen, who served as the White House butler for 50 years.
The all-star cast includes Forest Whitaker as Allen and Oprah Winfrey as his wife, while Jane Fonda portrays another First Lady, Nancy Reagan.