The see-through dress was worn by the princess-to-be for a 2002 charity fashion show while she and William were students at the University of St Andrews and is often suggested as the dress that helped Kate catch the prince's eye.
It had initially been expected to sell for between £8000 and £10,000 but global interest in the royal couple pushed the final price to more than six times the estimate.
Charlotte Todd who designed the dress has previously stated: "I never would have imagined as I sat knitting this piece that one day it would be so important."
What do you think? Is it a piece of fashion history or has the world gone wedding mad?