What to do if you filed married with IRS but found out you are not legally married?

If you filed your taxes as married but later discovered you're not legally married, you should file an amended return with the IRS using Form 1040-X. Change your filing status to "Single" or "Head of Household," depending on your situation. Ensure you recalculate any tax liability or refund due based on the correct filing status. It's advisable to consult a tax professional for guidance specific to your circumstances.