Can a will be challenged because of fraud?
A will can be challenged on the basis that a person prepared and executed that will because of fraud committed by someone else. If one were successful in this will contest, the will would be deemed entirely invalid. The specific requirements for fraud vary from state to state, but generally, to successfully show such fraud you have to be able to show that someone made a false representation to the deceased knowing the statement was false and intending to deceive the deceased, that the deceased reasonably believed this false statement and, as a result, executed a will that he or she otherwise would not have.
This fraud can typically occurs in one of two ways. First, there can be fraud in the document. This could occur, for example, if someone lies to you about what you are signing, so that you do not know you are signing a will, or if someone changed the provisions of your will before having you sign it. In addition to fraud in the document itself, there can also be so-called fraud in the inducement, which is where someone induced you to believe something which caused you to execute a will you would not have otherwise executed. For example, if your son tells you repeated lies about his sister in an effort to get you to disinherit her, this could be considered fraud which might invalidate the will (assuming you ended up drafting a will which did, in fact, disinherit your daughter).
It should be noted that the key distinction between fraud and mistake is that with fraud, there is somebody else involved, whereas mistake is all about the person drafting the will just being mistaken about some fact or law.