It was important both as a movie prop and as a fine example of Fifties couture.
Hepburn always asked her friend Hubert de Givenchy to make extra large seam returns in dresses she commissioned so that friends, to whom she passed them, could have them altered.
The gown had been altered over the years by a friend and then her nanny but all changes were expertly reversed.
The gown, with sky-blue satin bow and layers of silk point d’esprit, was back to its original condition when it attracted fierce phone and online bidding before going to an overseas buyer at £42,000.