Even if you agreed, he could not legally claim the child for these reasons:
1) The child cannot be his Qualifying Child dependent because the child did not live with him the required more than 6 months of the year.
2) The child cannot be his Qualifying Relative dependent because you CAN claim him as a Qualifying Child Dependent even if you choose not to so claim. The fact that you CAN claim as a Qualifying Child precludes anyone else from claiming as a Qualifying Relative.
3) You cannot agree to release the dependent under the rules for separated parents since the child is over age 18 and is an adult in almost every state and those rules cease to apply once the child becomes an adult. So unless you live in one of the few states with a higher age such as IN or NY. And releasing the dependent, even if you do live in one of those states is at the option of the parent that the child lived with.
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
