The IRS has their own rules on that, and those rules can not be overriden by any legal authority what-so-ever, below that of a federal judge. Most likely, you are the one who qualifies to claim the child anyway. See IRS Publication 504 and start reading on page 9 of that document. The section you want to start reading is 2nd column of page 9 at the bottom of that page, titled "Children of Divorced or Separated Parents (or Parents Who Live Apart)"
