I think she has a moral right to know whether he is her father. As you mentioned below, maybe she’s not, in spite of his having paid her mother. She deserves to know.
I sympathize with his wife, but the lack of scientific proof doesn’t make him a better husband.
I was thinking that could be the reason. Now that it’s all out in the open, I wonder if they could ever have a relationship, and if his three children would with her.