Princess Diana could not bear the existence of her 'wicked' step mother.
Diana's father, Edward John, married Raine McCorquodale in July 1976 without the approval of his first wife, Frances Shand Kydd.
Journalist Tina Gaudoin reveals Diana did not take the decision well and went on to 'slap' her father.
"All the Spencer children behaved very badly to Raine, it wasn't just Diana. They were purposely ganging up on her," expert Ingrid Seward admitted in 2017.
Later in her marriage to Prince Charles, Diana had a spat with Raine, causing her to push the 'wicked step mother' down the stairs.
Raine's personal assistant, Sue Howe, reveals the cause of the altercation was Diana feeling her original mother, Frances Shand Kydd, was not paid enough attention at brother Charles Spencer's wedding at Althorp House.
Ms Howe said: "[Raine] was badly bruised and dreadfully upset. It was not justified at all, it was a cruel heartless thing to do and I think it was Diana's perception of how Raine was treating Mrs Shand Kidd. I think Diana was very stressed. This sounds really wrong but she wasn't centre of attention on this occasion."
Royal biographer, Ingrid Seward, added of the incident: "She had a furious row with Raine because Diana was so upset that her own mother had been ignored in the ancestral home. She pushed her and Raine fell down the stairs."