My companion believes he's had a child with a woman from a relationship a few years prior. They were together when she said she was pregnant; he was there up until the birth of the child with the mindset that child was his. She has never let him see this child from the start of labor, as well as made it completely impossible for him to send in tests to start a legal process to begin any chance of custody.

My main objective putting this concern on the internet is, where does he start? What steps can you take (within a reasonable cost; younger adults) to begin a process of knowing where to locate your potential child?

((I have searched several things online to find any advance in ideas of how. Several options come up to be child abduction etc.))

Thank you for your reading and anything helps in the search!