Fraudulent Calumny
The recent case of re Boyes (Deceased), confirms that a Will can be set aside for fraudulent calumny. This legal principle is similar to undue influence, save that instead of being brow beaten into making a Will, in fraudulent calumny, a person is lied to about someone and on the basis of those lies, changes their Will.
In the case of re Boyes (Deceased), the Court found that the person was not in fact lied to. They genuinely believed that the Claimant was a bad person. The fact that they were probably mistaken was not enough to set aside a will.
Where someone thinks very badly of someone, even if they are wrong, they are entitled to disown that person in the Will. It is only if the deceased came to that decision through having their mind poisoned by someone else that the Will can be set aside.
Being wrong is alright. Only being lied to is wrong.