Many many years ago my DS had a girlfriend who I couldn't stand, and while I was quite accommodating to my childrens boy/girl friends I refused to have anything to do with this particular girl, we lived in a village at that time so everyone knew everyone's business and this girl had an awful name.Eventually she left the village and went abroad and I was so pleased. My son joined the RAF, something he had always wanted to do and was posted nearby so came home at weekends, then all of a sudden he stopped coming home, to cut a long story a bit shorter it transpired she had returned to UK and they were in touch again, then she said she was pregnant. My son said he was going to marry her and I refused to go to the wedding. They did get married, the boy was born but as they were now living in Scotland where my son had been posted to I didn't see or hear much about them. Eventually they came back south and on my sons 21st birthday my sister and I went to see them, it was the first time I had seen the boy and when I got my son on his own I said there was nothing I could see of him in this child. She continued her nasty ways, sleeping with many men while my son sat at home babysitting, until eventually he got fed up and they split up, he continued to pay for the child. He eventually married again and the 1st one kept causing trouble for him, so he eventually did have a DNA test done and it was proven he was not the childs father. the only thing you could do is to speak to your son on his own and tell him your feelings, it is then for him to decide if he wants to have the DNA test done or not. you shouldn't go behind his back and do it for him.