Jessica Chastain Oscars Dress: Happy Birthday, Mr. President!

Wearing a stunning Armani Prive beaded dress, Oscar nominee Jessica Chastain looked the polar opposite of her CIA agent character in Zero Dark Thirty.

"I'm such a fan of movies, I just love cinema," she told Ryan Seacrest of the inspiration for her dress. "It's a very 'Happy Birthday, Mr. President' kind of dress."

"It reminds me of old Hollywood glamour."

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Channeling her inner Marilyn wasn't an easy call.

Chastain admitted it was "a very tough decision" picking out a dress this year, given the number of options on the table now that she's a Best Actress nominee.

Along for the red-carpet ride? Jess' grandmother, who said she couldn't be more proud. "Twice in two years? This is so cool," the cool Michael Kors-clad granny said.

Sadly, the 35-year-old Chastain isn't keeping her accessories.

Showing off her Harry Winston bracelet, she confessed it would indeed have to go back Monday morning. But, she added, "We'll see if they can find me at 10 a.m."

Hopefully they don't have to send a repo guy after her.

Either way, her gown is widely considered to have been one of the best of the 2013 Oscars ... something the Anne Hathaway Oscars dress can't claim.

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