Mr Fayed’s father, Harrods boss Mohamed al Fayed, won an extraordinary High Court victory over the way the inquests are conducted.
Mr al Fayed won an unprecedented ruling overturning deputy royal coroner Baroness Butler-Sloss’s decision that she would sit alone.
Three senior judges ordered that the coroner hearing the inquest ‘shall do so sitting with a jury’.
Lady Justice Smith, sitting with Mr Justice Collins and Mr Justice Silber, made clear that Lady Butler-Sloss, if she continues hearing the case, cannot sit as the royal coroner.
The judges said: ‘We quash the decisions to conduct the inquests as deputy coroner for the Queen’s Household and without summoning a jury.’
The judges ruled that the coroner ‘shall reconsider the district in which the inquest shall be conducted in the light of the judgment’.
But they rejecting calls for Lady Butler-Sloss to stand down from the case.
‘We repeat that, in our view, there is no reason at all why Lady Butler-Sloss should not continue to conduct these inquests,’ they said.
The princess, 36, and Dodi, 42, died when their Mercedes crashed in the Pont de l’Alma tunnel in Paris in 1997 as they sped away from pursuing paparazzi.
Mr al Fayed said he was ‘certain’ Diana and Dodi were murdered and welcomed the High Cour ruling. He said: ‘This is not the end of the road, but an important step.
‘The jury must now be allowed to hear the entirety of the evidence, but I fear there will be attempts to keep it from them. If so, that will be yet another battle I will have to fight.
‘I have already had to fight for almost ten years to establish once and for all how they died, why they died, who ordered their murders and who slaughtered them with such awful brutality.
‘This is my duty as a father. I shall not fail Diana or Dodi, though the barriers erected against me have been many and formidable.