The Duke of Cambridge, 39, told his mother he would restore her Royal titles after she finalised her divorce with Prince Charles in 1996. While the couple had separated four years prior, in 1992, their divorce led to one big change for Lady Diana.

       She lost the 'Her Royal Highness' title.

       Diana became 'HRH The Princess of Wales' after she tied the knot with Prince Charles in July 1981.

       But a former butler to the People's Princess claimed her eldest son's commitment to return the HRH title reduced her to tears.

       According to The Mirror, Queen Elizabeth II was happy for Diana to retain her titles.

       However, Prince Charles was said to have insisted they were removed.

       Diana then became known only as 'Diana, Princess of Wales'.

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       The change meant friends and staff would no longer be obligated to curtsy or bow for Diana.

       It also meant she would have to curtsy for members of The Firm, including her ex-husband.

       Lady Diana was allowed to keep her apartments in Kensington Palace and received a substantial sum in the divorce settlement.

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       However, William was unable to restore Diana's titles as she tragically passed away the following year.

       Diana died at the age of just 36 in August 1997 when she was involved in a car crash in Paris.