Princess Diana's will is to be made public this week and her lawyers are expected to apply to vary it to make it easier for the princes to inherit her estate.
It is understood her current will, drafted before her divorce from the Prince of Wales, only allows the princes to inherit the estate when they reach 25 years.
Lawrence Graham partner Martyn Gowar, who is acting for Diana's estate, said that "for various reasons", this created difficulties in passing her estate on and that the terms of her will had to be effectively redrafted.
He said this was no criticism of Mishcon de Reya, Princess Diana's advisers during her divorce, since in the emotive circumstances of the separation she would have been unlikely to want to redraft her will.
The will of the monarch is kept secret but the wills of all other individuals have to be freely available to the public.
Mishcons partner Chris Allen asked Gowar to represent the princes last November when it became clear there would be a conflict of interest if Mishcons acted for both the Diana, Princess of Wales Memorial Fund and her estate.