Paying for child support when ex-wife lied about kid and dna testing shows non-biological relations?

Maybe not, especially if your brother lives in Florida.  The Supreme Court there recently held in a case on appeal that a man must continue to pay child support to his ex-wife for another man’s child, even though DNA evidence proved that the child was not his.  Family courts traditionally look first at what is in the best interest of the child, putting the needs of the child above one parent defrauding the other.  Florida Supreme Court Justice Kenneth Bell wrote in his opinion that although the former husband might feel victimized, “While some individuals are innocent victims of deceptive partners, adults are aware of the high incidence of infidelity and only they, not the children, are able to act to ensure that the biological ties they may deem essential are present.”  Your brother should seek the advice of a family law attorney to gain insight regarding the precedence of this issue in his state.