Queen and 'disloyal' Diana

Two of the Queen's closest friends have told a TV documentary how she could not cope with Princess Diana's mental instability and the breakup of her marriage to Prince Charles.

Lady Penn, a former lady-in-waiting to the Queen Mother and the Queen's cousin Countess Mountbatten, claims that in private Diana was very different from her public image and that the Queen found the break-up of Charles's marriage hard to understand.

The candid interviews, which royal watchers believe must have received tacit approval from Buckingham Palace, will be screened on ITV on Tuesday 4 June, after the Queen attends a thanksgiving service at St Paul's Cathedral and watches the Jubilee pageant.

Lady Penn says in the programme: "The Queen found Diana's ill-health or mental instability very hard to understand because she's a very matter-of-fact, down-to-earth person.

"The Queen tried very, very hard to understand and help when the relationship between Charles and Diana began to deteriorate, but it was not an easy thing for her."

According to Lady Mountbatten, Diana convinced herself Charles was still seeing Camilla Parker Bowles when he was not.

She says: "Absolutely nothing he could say or do would disabuse her of the idea that somewhere she was lurking in the background, which was an absolute tragedy, because it was totally untrue."

Diana's role in Andrew Morton's book about the marriage is said to have left the Queen shocked. Lady Mountbatten describes the "feeling of disbelief that somebody within the family could do something like that and be so disloyal".