Both spouses are usually liable for tax owed to the IRS on a joint tax return but one spouse may be able to avoid tax liability to the IRS through the application of what has come to be known as the "innocent spouse doctrine." Under this tax doctrine, a spouse may be excused from tax liability to the IRS for tax and/or tax penalties.
The 1998 tax law broadened the definition of "Innocent Spouse Relief" so that relief from IRS tax liability is now more available for those spouses who filed tax returns jointly, yet the circumstances demonstrate that it would be unfair for the IRS to hold both spouses equally responsible for the joint tax liability. In many of these tax cases, a spouse is relieved of responsibility to the IRS for tax, interest, and tax penalties on a joint tax return. This is called innocent spouse relief.
Under the circumstances of what you have described, you should file a claim for Innocent Spouse Relief with the IRS.
I am giving you a link below to IRS Publication 971 which will give you complete details on how to file this form.
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