A child born while the two of you atre married is legally presumed to be yours. In a divorce and in a child support case you will be made to pay child support unless you disprove paternity. Taht willl require two things: (1) you have to ger a lawyer and should have already hired one, and (2) you will have to request and probably pay for DNA testing. This is an issue you should have raised in your ansswer and counterclaim (hopefully in the first 30 days of your case.)
Whatever you do, you need a lawyer, and you need him yesterday. Drop whatever you planned for Friday and hire one. This is an emergency that requires your immediate attention.
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I agree with my colleague that having a child born during the marriage gives rise to the presumption that you are the biological father. You will need to disprove this with a paternity test.