What do I do

My boyfriend and I have been together for 2.5 years we have a child together and have discussed our future together well the other day he got a letter from the attorney general some girl is trying to put him on child support I asked him if he knows about the kid he said no she never told him that the child was his and they haven't talked in years. The baby was born august 2017 I'm just in shock like how am I supposed to feel about this of course I have a ton of questions be seems to not care about it at all they have a court date monday he is going to ask for a DNA test. My thing is why did she all of a sudden want to try and put him on child support 2 years later. The girl has 4 kids I feel like she is just trying to find who her baby daddy is. I dont think my boyfriend is lieing about not knowing he has another child which hes told me about plenty of times and there was another he raised but she turned out not to be his it just bothers me that he seems to not care about it. Idk what to feel my mind is all over the place.

Also for anyone that has been through this will he have to pay for the paternity test? Or could you give me a little insight on how the whole process works.