The reason behind feuding between mothers-in-law and their son's wife has been answered, wives are programmed to dislike their partner's mum.
It's the age-old power struggle that blights millions of marriages.
In a new book, that has just arrived Down Under, Dr Terri Apter, a psychologist and senior tutor at Newnham College, Cambridge in the UK, has suggested that even if a wife or girlfriend wanted to like her in-law, she already had an expectation they wouldn't get along, reports The Daily Telegraph.
Relationships Australia NSW (New South Wales) chief executive officer Anne Hollonds said: "It can be a great source of conflict and part of the problem sometimes stems from issues between the mother and son. The (issues) have not been resolved when he starts a new relationship.
"Instead of the husband sorting out the relationship with the mother and his wife, he will stand aside and let the women fight it out."
To reach her conclusion, Apter interviewed more than 200 people, including 49 couples.
The analysis revealed that almost two-thirds of women complained they had suffered long-term stress because of friction with their husband's mother.
Dr Apter said both women assumed that each was undermining the other.
"This mutual unease may have less to do with actual attitudes and far more to do with persistent female stereotypes that few of us manage to shake off completely," she said.
"Both mother and wife are struggling to achieve the same position in the family, primary woman," she added.