Prince William was left deeply upset by the Panorama interview in which his mother princess Diana lifted the lid on her marriage to Prince Charles after she had assured him it would contain nothing controversial, a new biography has revealed.
The Princess of Wales was interviewed by BBCs Martin Bashir in the current affairs program Panorama on November 20, 1995.
A 13-year-old schoolboy at the time, young William watched the programme in the study of Andrew Gailey, his house master at Eton, claims the book by Penny Junor.
Gailey was said to have insisted that Diana explain face-to-face what she was about to do after learning about the BBC interview, and she eventually reluctantly agreed to go to the school.
The meeting lasted no longer than five minutes, during which she assured her son that the interview would not contain anything controversial and would make him proud of her, according to Junor.
But the young royal was said to have been left in disbelief by the succession of startling claims made by Diana, to an audience of 20 million people, including the revelation that There were three of us in this marriage.
Not unnaturally, he was deeply upset, the Telegraph quoted the new book as saying.
By the time William emerged from Dr Gaileys study, he was angry and incredulous.
How, he must have asked himself, could his mother have done such a terrible thing? it said.
The revelations have been published in the biography Prince William: Born To Be King: An Intimate Portrait, serialised in the Daily Mail.
The book also says that the Royal was caught up in a number of incidents of marital one-upmanship as his parents relationship descended into acrimony.