what if other parent claimed child but wasn't supposed to

Ex-spouse agreed to allow me to claim my child but he claimed her anyway.  How do I get the Irs to dispute his Claim?
    For divorced or separated parents, the custodial parent who the child lived with for more than half the year, can claim head of household filing status, child care expense credit, and earned income credit. The non-custodial parent, if allowed by divorce decree or consent of the custodial parent, can claim the dependency exemption and child tax credit. The child tax benefits cannot be split any other way.

    If you were not the custodial parent, there is not much you can do. If you were the custodial parent, you can file a paper return and the IRS will sort out who can rightfully claim the child.
    • Thank you for your answer.  Do you know if I will need any proof?  You see, last year we agreed that I would claim one of our daughters and he would claim the other.  They have his address because they wanted to stay in their same schools.  I haven't really got any thing saying I can claim her other than he signed some form last year saying I could.  Now this year he conveniently forgot about that and claimed her anyway.
    School address is one of the forms they ask for to prove who the custodial parent was. If he is the custodial parent and will not sign form 8332 releasing the dependency exemption to you, there is not much you can do.
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