Legal Question in Business Law in California

It's certainly at least a possibility......just about any document or instrument signed or obtained by fraud can be overturned in court. The quality of proof required, the time to act, and other factors may vary from situation to situation. When two or more persons are partners (or otherwise locked together in a close business relationship), they owe one another an especially high degree of fairness in their dealings (they are in a so-called "fiduciary relationship"). You should seek an initial consultation with one or more business lawyers (rather than personal-injury specialists) to have your facts evaluated for the necessary elements of fraud and the sufficiency of the proof you can provide to support your claim in court.

The answer is "maybe". But can you prove that it was fraud? That's where you need to consult with an attorney and seek further advice.