Tax lax, which party gets to claim the mortgage interest?

In divorce I received the house, both equity and debt. I made the joint mortgage payments (4months) until I could get the loan refinanced into my sole name. These payments were all made after the divorce was finalized. Who gets to claim the mortgage interest for those 4 months? Me, since I made the payments and have the proof of payment or my ex who was the primary on the joint loan? What if we both unknowingly claim that interest, who does the IRS side with?

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