A will is fraudulent and therefore invalid (either completely or in part) if it has been created or changed by someone other than the will-maker and without the will-maker’s approval.
Fraud can also occur where a person misleads a will-maker, either as to the person’s character, conduct, or personal circumstances, so as to obtain a benefit under a will. Any part of a will that resulted from such fraud is invalid.
Read about the process to challenge the validity of a will on the basis of fraud here.