I found out I was a father a few months ago after I took a mail off dna test. The mother and husband are currently going through a divorce and he wants half custody of my son?

What can I do?

And your location is..?
The law varies from state to state

In some areas there will be nothing you can do, and at this point if he is listed on the birth certificate and/or if he was married to her at the time of birth, he is legally the father, and it is his child until that is proved not to be the case in court.

Some areas will not even allow you to contest it, if they were married at the time of birth.

So you need an attorney at this point

ANY question about law NEEDS to include your general locale as laws vary by area.

In almost all areas, when a child is born to a married couple, the husband is considered the legal father. The only way to change that is to mount a court battle for custody. However, depending on where you are, the time frame for doing so may have passed.