You cannot claim the child because the child is not related to you and did not live with you the entire year (only 9 months).
Even if the child did live with you the entire year, you could only claim the child if the mother was not required to file tax return because the child would then be her Qualifying Child that would prevent you from claiming an unrelated child, even if she choose not to claim him.
The father could only claim the child exemption if the mother (the custodial parent) chooses to release the exemption to him with a signed 8332 form. Only a court order could compel her to do so.
**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.**
