The answer is "maybe" or "maybe not" depending upon some important facts which are missing here. If your aunt was susceptible to influence due to age, illness, etc., then that would help your position. Similarly, if your nephew was in a position of influence, such as a caretaker for your aunt, and he used that position to direct your aunt to an attorney of his choosing for changes to her documents, that would give you additional facts toward demonstrating undue influence. That said, undue influence is not always easy to prove, even when there is evident age or memory issues. You will want to see a lawyer in your area or the area your aunt lived in and describe the details for an analysis of your case.
You could contest the Trust on grounds of undue influence but since you are not a natural born heir to your aunt, as opposed to being her daughter or son, you'll face a difficult time proving that she was unduly influenced in leaving you nothing in the Trust. I would have to know more about the relationship you had with your aunt versust the relationship her nephew (Is he your cousin?) had with her.
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To contest the trust you would have to prove that the trustee was in a position of confidence as to your aunt and somehow used that confidence to convince her to remove you as a beneficiary against her own wishes. These cases are extremely difficult to prove, and you are at a disadvantage because you are not a "natural object of her bounty" as a son or daughter might be. There are also limitations periods as to contesting trusts. If you believe you have proof that the trustee exercised fraud, duress or undue influence over your aunt, you should consult an attorney in your area as soon as possible.
This is not intended to be legal advice nor to create an attorney/client relationship.