From what you're describing, there may be nothing "ironic" about this -- you may have a clear-cut case of undue influence and/or a will made through fraud.
Go to the courthouse and get a copy of the will and anything else on file, then go see an attorney who specializes in probate litigation. You want to determine if there are grounds to overturn the will.
Thanks for your question. Since your brother benefited from the change in the will, if he was managing your uncle's finances or was otherwise involved in his care, the burden shifts to him to demonstrate that the change in the will was NOT the product of undue influence. However, you must take the first step by challenging the validity of the will. There are strict deadlines for doing this and the failure to adhere to those deadlines can be fatal to your claim. Please see my blog at www.lawfang.com for details about challenging a will and specifically the use of an undue influence argument.
The law of what constitutes undue influence has been changing over the past decade. At this point, the burden of proof may well be on your brother.
The 2008 Massachusetts case of Germain v. Girard has made it easier to challenge estate plan changes on the grounds of undue influence. Because of Germain and other recent case law developments, the burden of proof when arguing the existence of undue influence is no longer on the person challenging estate plan changes. If a person who was in a fiduciary role or other position of responsibility received a direct or indirect benefit from a transaction, that person is now in the position of defending the transaction.
A large part of the court’s concern in Germain was that the lawyer drafting the new provisions was taking instructions from someone other than the person who was eventually going to sign the document. Therefore, lawyers who prepare documents are now being held to higher standards to make sure elderly and disabled persons are being protected.