Your rich and -- you thought -- loving relative died, but when his last will and testament was read you were left not a penny. If you stood to gain something from a will but were left out, you can challenge the will in court as a first step in invalidating the last will and testament and getting what you see as your fair share of the estate. A will may be invalidated by a court for several reasons, although many are difficult to prove, and the legal challenge in probate court can be complicated. Hiring a lawyer to guide you through the process can be beneficial.
Go to the probate court handling the estate and check the paperwork. The law says important formalities must be followed when executing and probating a will. The original of the will must have been filed in court. The testator -- the person who filled out the will -- had to have signed the will at the end, before witnesses (at least two, in most states). The testator also must have manifested to the witnesses, in some way, that he was signing his last will and testament, though he didn't have to share the contents with them. And finally, the witnesses must be disinterested -- if the will says the witnesses share in the estate, their testimony won't count.
Challenge the testator's capacity to execute a last will and testament. The law says he had to have "testamentary capacity." That means he had to be an adult of sound mind. "Sound mind" means that the testator had to know about the estate he was leaving. He also had to demonstrate some idea that he knew who his natural beneficiaries were, such as his children, even if he meant to cut them out. The last will and testament also had to contain an orderly estate plan, so the probate court can understand who gets what.
Question whether an outsider exerted "undue influence" over the testator. That means the outsider had such a hold over the testator that it affected who got what in the last will and testament. Undue influence is another grounds for invalidating a will. You have to show that the outsider so overcame the testator's mental will that his written will forced the testator to give his property to someone who would not usually have received it.
Prove fraud. Fraud is another reason to invalidate a last will and testament, but it can be tough to prove. Show that the fraud rose to the level of a crime -- such as the fraudster telling the poor old sick testator that his beneficiaries died but they wanted him to leave all his money to the fraudster, or that the fraudster forged the actual pages of the will to change the estate plan.