Audrey Hepburn was a British actress and humanitarian. She is most known and endlessly imitated for her role as Holly Golightly in the film adaptation of Breakfast at Tiffany's. She is recognized as a cultural icon and has become the standard for beauty in Hollywood.
Damien is kind of obsessed with her; yes, even more than Kate Beckinsale.
James, while not as familiar with her work as Damien, has gone on record multiple times as stating that she is the most beautiful woman that ever lived.