Did your son make less than$4,050? If not, then you won't be able to claim him. If he did make less than that, then he would have to amend his tax return and remove his exemption in order for you to claim him.
The amending process takes a long time (up to 16 weeks). Mailing your return would be required if you plan on claiming his exemption before his amended return is complete. You won't be able to efile. See some other useful links below.
Who can I claim as a dependent?
Does my dependent have to live with me?
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