My husband wants to bring his mistress' child home. what should I do?

Dear Counsellor,
We have been married for 10 years. We met when we were at university. We have one child. About four years ago, when my child was seven months old, I discovered that my husband was having an affair.

His mistress even called to let me know my husband shared with her all our plans. At that time, we were constructing our family home,  she told me she is aware of it and that my husband would build one for her as well.

I confronted my husband, but he denied being involved with her. However, his mistress kept harassing me. At one time she told me that I was working for her. That’s why my husband used to give her the money I used to give him. 

Fortunately, the affair ended and sources close to her say she went back to her village. They say she is suffering since it was my husband taking care of her.  

I thank God He saw me through that tumultuous period and today my husband and I are happy.

However, my husband had a child with his mistress. My in-laws say he told them he wants to bring that child home, but he’s afraid of my reaction. I can’t imagine living with a child whose mother and her people wanted me and my child dead. What should I do?
Samantha