@mistercm83 : yes, the fact that you lived together, even if legally divorced, prevents you from splitting the tax benefits. Only one parent can claim the child on his/her taxes. But, it can be either of you (so long as the child lived with you more than half the year, 183+nights) and you can agree on which parent will claim the child. If you can't agree, then there are "tie breaker" rules that govern.
"What would I need to show the Irs possibly to prove this?" You need to show that the other parent didn't claim the EIC, based on that child. You may also have to prove that the child lived with you.
