What would you do?

Long story, My now 20 year old son's biological father has not played a roll in my son's life. He was not around including the pregnancy. He popped back in and out of his life various times in his early years, I allowed and encouraged him to try and build a relationship, but it only ever lasted a few weeks. (Birth, around 3 and 5) My son has snippets of memories of these times. Until my son was 12, I actually only lived around the corner from his Bio father, I only moved a big distance away at that point but told the Bio father where we moved. Our number has always been listed. My son was also raised by another man from very early on who has done everything a father should do, and in my son's eye's he see's him as his Dad. He was raised to know the truth of his parentage, never has anything negative nor ill feelings been told to him. When my son was 9, the bio father tried to pop back into his life and I asked my son if he wanted it and he said no. I kept the communication lines open with the bio father, he knew he could call and I would always be honest about my son in regards to schooling his personal activities etc, there were time's I actually spoke to my son directly while on the phone to him so he could hear my son's responses. I always have supplied pictures of my son over the years. That came to a halt when my son was 15, his bio father tried to contact him directly through Facebook and the result was less than desirable. My son was already dealing with Teen growing pains so to speak and was not ready nor wanted the contact. It was a very rough ride for all involved. In the best interest of my family and my son, I had to stop allowing him to contact me directly but offered an alternate contact person. He never made contact again.

Fast forward to 6 months ago, I received a message via inbox from a woman, who in fact is my son's bio father's de facto and mother of his new child. I took her at face value and expressed my concerns over the contact. She wanted to ensure my son knew of his sibling, and that his bio father was a good man now. They wanted to let him know that he was welcomed to be apart of their lives when he was ready. I filled in the last few years of my son's life, and how well he was doing now. I talked to my son about his sibling, showed him pictures. I actually encouraged him to make contact as he has a chance to be around his sibling and build a relationship. (I am a strong believer that siblings should be an active part in each other's lives, I have seen so many kids torn apart and grow up with out knowing each other.) My son was hesitant and she said when he is ready, no expectations. On and off I received messages from this woman, the picture she painted was up and down, on and off, drug use, cheating, violence. I have kept this all to my self as I want my son (now an adult) to be able to use his own judgement and go with a clean slate when the time arises.

Well now, that time has come, my son is moving closer to them due to his career path and he asked me for contact information. I messaged this woman letting her know and the reaction I received was not so good. She has said that they are denying my son is his, that they want nothing to do with him and a lot more not so nice things thrown in. I have yet to tell my son this. I'm not so sure how to go about it. My Husband wants me to allow him to read the Facebook conversation that spans back the 6 months. I'm not so sure that is the best move. I am at a loss, I have spent the last few months encouraging my son and supplying the update's to him and now they have the result they wanted when they first reached out they are slamming the door closed. In their words too little too late.