That's the $6billion question. All eyes will be on soon-to-be Princess Catherine in two days' time as she climbs out of the car with her father. Everyone's expecting a demure dress with sleeves. But the certainty ends there. Will she wear a tiara? Will it be a slim-line dress? Or a puffy dress? Will she wear a lace veil? How long will her train be?
Here are some dresses worn by Princesses on their wedding days for some clues.