[AK lawyer]

Good question.

Another one: why have they suddenly moved next door to OP. Much more than a coincidence, I think.

Or perhaps when OP wrote "LITERALLY right next door to me", he didn't mean it literally, i.e.: in the house next door. Many people mis-use "literally" when they really mean just the opposite (figuratively). If they are close by, perhaps in the same town or neighborhood, it wouldn't be such a coincidence.

In reviewing what OP has written, I see that a woman with whom he had been intimate got pregnant and, just before giving birth, broke off contact with him. She had indicated that the child was his, but disappeared. She made contact with OP once every few years thereafter. Presumably OP knows that the man now raising the boy is the woman's husband. Thus it would be reasonable to assume that the boy might be OP's natural son.

If this is the case, I suggest that he might contact an attorney &/or a detectvie for the purpose of (in no particular order) determining what happened to the woman, whether the man has any legal rights to the boy, and going to court to establish paternity and (if so) visitation rights and child support obligation.

... People don't completely disappear, especially wealthy people. A good PI would have found them. ...

If you don't want to be found, in many respects it would be much easier to hide if your parents have a virtually unlimited bank account and are willing to write checks for whatever you need. OP might have asked the parents where she went and they could have simply ignored him. And such a PI would be beyond the means of many folks.

[talaniman]

I believe the overriding issue is what's in the best interest of the 15 year old child since any legal action would take months and years not days and weeks and any court order would involve a paternity test. It's a mess and a huge can of worms to be opened, and no doubt disruptive for many for who knows how long. Much to far reaching for emotional, impulsive responses legal or not.