Probably not. Your son is probably not a qualifying dependent of anyone besides you or your ex. The IRS wants to know who the child spent the most nights with. Technically, your ex or someone else could process a tax return claiming your son and get a refund. However, if you are entitled to claim your son, whoever erroneously claimed your son would have to pay the money back and could be penalized. So although it possible that someone who should not claim your son, does so, the IRS will take action against taxpayers who wrongfully claim a dependent. Here are the requirements for claiming a child as a dependent on your tax return.
https://turbotax.intuit.com/tax-tips/family/rules-for-claiming-a-dependent-on-your-tax-return/L8LODb...
You can claim a child, relative, friend, or fiance (etc.) as a dependent on your 2018 taxes as long as they meet the following requirements:
Qualifying child
- They are related to you.
- They aren't claimed as a dependent by someone else.
- They are a U.S. citizen, resident alien, national, or a Canadian or Mexican resident.
- They aren’t filing a joint return with their spouse.
- They are under the age of 19 (or 24 for full-time students).
- No age limit for permanently and totally disabled children.
- They live with you for more than half the year (exceptions apply).
- They didn't provide more than half of their own support for the year.
