This dress is Sabrina (Audrey Hepburn's) Grand black and white ball gown. It would also not be amiss at a modern day wedding. The double skirted dress has a giant floofy train that would satisfy an elegant bride.
This movie has one of the most famous movie wedding gowns. However, much ignored is the rose gown from an earlier fashion shoot portion of the movie. This would also make a very princessy gown.