True Confession: How do I tell my husband I’m pregnant for his father?

I am a mother of three, presently pregnant with my fourth child.

My husband thinks he is the father of my unborn child but in the real sense of it, the child is his father’s.

I and my husband are happily married for 11 years he left three years ago in search of greener pastures in USA, since then I have been having sex with his father because I think it's better than cheating on him, my husband visited home 8 months ago and before his arrival I was already two weeks pregnant for his father but I didn't tell my husband so after we made love and he returned to USA, I told him I was pregnant and he is so excited thinking it's his child💔

How do I tell my husband the truth, he has been super caring, provides for me and my entire family,he even built my parents a house,now the X-ray shows it's a boy and we have 3 girls and have wished to have a baby boy, I tried abortion twice I almost lost my life .

Now my husbands father says we should keep it a secret to my husband which is impossible because he is filing for us to join him in the USA and the embassy needs a DNA test, since it's my husbands dad who is responsible will the DNA results proof it's my husband?

Please advice me on how to get out of this mess.