Diana stipulated in her will that the silk and taffeta lace dress, designed by David and Elizabeth Emanuel, should be given to her boys once her youngest, Prince Harry, turns 30. He will reach the age milestone on 15 September (14).
The iconic outfit, which featured 10,000 pearls and boasted a 25-foot (7.62-metre) train, has been in the possession of the late princess' brother, Charles Spencer, since Diana lost her life in a car crash in Paris, France in 1997.
He previously used it as the centrepiece of the Spencer family museum at Althorp in Northamptonshire, England, where it remained on display for over 10 years from 1998.
It is not yet known what Princes William and Harry plan to do with the dress.