Princess Diana once faked falling down the stairs while pregnant with Prince William because "she wanted attention", Paul Burrell claims.
The Princess of Wales's ex-butler alleged the cry for help came in 1981 when she was four months pregnant with her first child.
Burrell - once described by Diana as her "rock" - revealed the incident on Channel 5's The Royal Family, Scandals at the Palace.
He claimed he overheard an "enormous clatter on the wooden staircase" before he found Diana "half way down it, faking a tumble while she was carrying William".
Burrell said Diana did it because "she wanted attention" - but insisted she did nothing to harm her unborn child.
The incident at the Sandringham Estate first came to light in 1992 when royal biographer Andrew Morton revealed she had done it in a desperate attempt to get Prince Charles "to listen to her".
Princess Diana's fatal injury 'was tiny, in the wrong place and incredibly rare'
The royal couple tied the knot at St Paul's Cathedral in July 1981 - and Prince William was born 11 months later.
Their marriage was rocked by allegations of cheating before Charles finally admitted he had been "unfaithful" in 1994.
The pair divorced in 1996 and the Princess died in a car crash in Paris the following year.
Last month the Royal Family At War documentary claimed Diana and Princess Margaret disliked each other and stopped speaking after the Princess of Wales revealed details about her marriage to Prince Charles shortly before their divorce was finalised.
And the programme also alleged the Prince of Wales is trying to sideline his brother Prince Andrew amid concerns he is "ruining" the Queen's legacy.
Royal biographer Penny Junor said: "Charles is worried that Andrew's behaviour at times is damaging the family firm."
