The Les Miserables star, who won the Academy Award for Best Supporting Actress, had planned to wear a gown by her good friend Valentino, but changed her mind after Miss Seyfried shared an iPhone snap of her own Alexander McQueen creation - which was very similar - during a rehearsal.
'Anne was like, "WTF?"' a source told Us Weekly. 'She started throwing a fit!'
'Anne made the fashion, make-up, hair, and jewelry teams wait at her home for hours as she decided what to do about the dress debacle'The decision backfired on her though, with her stylists and beauty teams objecting to the wait as she agonized with stylist Rachel Zoe over the selection of a new gown, a second source told Us.
'Anne made the fashion, make-up, hair, and jewelry teams wait at her home for hours as she decided what to do about the dress debacle,' they said.
And after trading her planned Valentino gown for a pale pink Prada creation, she was forced to issue a public statement by way of apology to Valentino, whose press team had already sent out a press release announcing her choice, unaware of the last-minute switch.
She insisted that the trade was not intended as a snub to Valentino, who designed the wedding gown she wore to marry husband Adam Shulman last September.
'Though I love the dress I did wear, it was a difficult last minute decision as I had so looked forward to wearing Valentino in honor of the deep and meaningful relationship I have enjoyed with the house and with Valentino himself,' she continued.
Memorable fashion moment: Valentino designed the romantic pale pink gown and headpiece that Ms Hathaway wore to marry Adam Shulman last September
'I didn't know what I was wearing until about three hours ago,' she told him. 'This was the one that spoke to me in the end.'
Her dress choice undoubtedly came as a surprise to Valentino, whose fashion house sent out a press release just before the awards show stating that it would be dressing Anne Hathaway, Sally Field and Jennifer Aniston.
Close friends: Valentino (pictured with Ms Hathaway in one of his designs at the 2011 Oscars) has said that the actress is 'like my daughter'The actress certainly caused a stir in her backless pink satin Prada gown - complete with a very perky bust line - which she accessorized with a sparkling Tiffany necklace.
Ms Hathaway has a long history of friendship with 80-year-old Valentino, who has said of the actress: 'She's a very good friend of mine. She's like my daughter.'
She has worn a number of his creations to awards ceremonies - including the bold red strapless number she wore to host the Oscars in 2011.