Is it wrong to demand a DNA test when your husband is on the birth certificate for someone else's baby?

I feel sick. My husband says he was "just helping out a friend" and is on the birth certificate of a baby born 10 years ago, two months after our child was born. I'm just finding out about this now.

This kid is his spitting image. Apparently the mom (a friend of his from highschool) is going through a hard time and is trying to get over $60k in child support back paid. My husband says that he only gave her his info to put on the birth certificate "as a favor", but I'm like, why the hell did you do that with a wife and newborn at home?!

He denies cheating and has never given me reason to believe he cheated. I so want to give him the benefit of the doubt but this kid is his spitting image and I'm only finding out about this now.

I told him to get a DNA test and he says he doesn't need one and he'll win in court. I said the kid is your spitting image, sorry, but I want a DNA test and I don't see how he won't be ordered to do one.

Please tell me I'm not being unreasonable. And where do we go from here? Obviously therapy but he's not taking it seriously at all.

Edit: ok so it's been a couple days and things have slowed down a little. I have been (admittedly) unhinged and told him he needs to find somewhere else to sleep for the time being. This is a lot to process!

He has agreed to a DNA test but has assured me it will come back that he's not the father. He says he will do a lie detector test if it means I will stay. I said ok, then why are you of all people on the birth certificate?

He came forward with everything, screenshots, everything. A signed document and like I said, EVERYTHING. The guy who is the child's father (allegedly) looks like he could be related to my husband so that's why this child looks like him.

Apparently my husband "helped" his friend because he has Native status and so he gets a whole lot of perks. The "friend" wanted her child to have those perks too (like not having to pay for college). That's the only reason he's on the birth certificate. It's so the kid can claim Native status.

I told him that's fraud. Plain and simple. I want no part of this. Apparently he was too stupid to realize that by having his name and everything on the birth certificate, she can now claim a whole lot more than just Native status!

For the time being we're living separately and I told him we need counselling. This is a huge lie he kept from me and if he had told me ten years ago about what he was doing, I would have put an end to it. I told my husband that at this point he needs a lawyer and to hope that everything he has (including signed documents from the woman saying that she will not claim child support) will hold up, but honestly, with his name on the birth certificate and all the other crap, I'm thinking he's probably going to have to pay that child support.