From my understanding of the IRS procedures, when the same personal exemption is claimed on two or more tax returns the IRS will send a notice to all parties requesting the information that you received. If neither party amends their tax returns to remove the personal exemption then the IRS will send another notice to require proof from each party that they were entitled to claim the exemption.
See this IRS 886-H-DEP for the supporting documents that are required - <a rel="nofollow" target="_blank" href="
https://www.eitc.irs.gov/eitc/files/downloads/f886-h-dep.pdf">https://www.eitc.irs.gov/eitc/files/do...>
The party that cannot prove they were entitled to the personal exemption must pay back any tax refund received based on that exemption plus penalties and interest.
