The 39-year-old actress went Cannes for the premiere of Armageddon Time. She donned a magnificent Armani Privé gown.
Hathaway tells a magazine, "You hire Erin Walsh and you trust her," about how to put together the perfect Cannes wardrobe.
"I've never been to Cannes, but I've been keeping up with the style of the film festival for over 20 years. And I've learned that there are some things that can never go wrong."
"A little sparkle never goes wrong. You can't go wrong with something that looks chic and glamorous but feels very, very comfortable.
And I noticed that a lot of my favourite actresses had worn all white before," the Les Misérables star went on. "Well, that's what I did."
Hathaway appeared on the red carpet solo and with her Armageddon Time cast in a strapless Armani Privé gown.
The back of Hathaway's gown included a show-stopping bow that extended into a long train, which she removed inside the theatre.
Hathaway completed her ensemble with the Mediterranean Reverie necklace, which she wore alongside her husband Adam Shulman at the Armageddon Time after-party.
"The magnificence of a rare stone - 107,15 brilliant carats of royal blue cushion cut sapphire from Sri Lanka," the piece from Bulgari's new Eden The Garden of Wonders High Jewelry collection.