755 ILCS 6/20-30: Evidence of fraud, forgery, compulsion, or other improper conduct.

Nothing in this Article prohibits any party from introducing evidence of fraud, forgery, compulsion, or other improper conduct that in the opinion of the court is deemed sufficient to invalidate the will when being admitted. The proponent may also introduce any other evidence competent to establish the validity of a will. If the proponent establishes the validity of the will by sufficient competent evidence, it shall be admitted to probate unless there is proof of fraud, forgery, compulsion, or other improper conduct that in the opinion of the court is deemed sufficient to invalidate the will.