How am I going to do this?

Hello,
A brief, brief as I can, background on this dilemna of mine. I am 50 yrs old, divorced, mother of 4 adult children. All who are my whole life, they are the air I breathe. When I was 18 yrs old, I got pregnant and the romance was just a teenage fling and the father wanted nothing to do with me then, and urged me to have an abortion and never contact him again. I never did contact him again, nor did I want to and I did not have an abortion either. I had my child, worked and went on with life. When he was about 2yrs old I met a man who adored my son, we married and my new husband adopted my son and life went on. Our plan at that time was to never tell my son because we were young, in love, raising a young family and of course as we all dream of, would be together forever. We had 3 more children. My husband was good to all 4 of our children as they grew, but as my first son got older my husband always seemed to be a little rougher on him, disciplined him more than our other 3 kids, and eventually my son and my husband grew apart and fought all the time. My ex and I divorced a few years ago. Fast forward to present day. My kids are grown now and the arguments and fights have gotten so bad between my oldest son and his father that they have completely stopped communicating for the past 2-3 years now. My son is hurt because he does call his dad on fathers day, or birthdays, and his dad will not take his calls and now, I have recently learned that my Ex has posted on his facebook profile that he has 3 children and 1 grandchild. There are 4 children of ours, and 3 grandchildren!!!!!!!! My ex also has not, and has no desire to see the 2 grandchildren that are from our, my oldest son. SO! Needless to say, my son feels that during the course of all the dumb choices he has made as a young adult, that his father has turned his back on him forever. My son cries over the mistakes he's made, but moreso that his father isnt there for him. My ex is a vengeful, spiteful one. My biggest fear is that HE , out of spite for me, will tell my oldest the truth in the meanest, cruelest way possible. I think, I know, we've kept this a secret far too long and I just have so many concerns. First being, as I stated, my son right now isnt in a good place. He has been in and out of trouble most of his adult life, and although some may say this isnt the right time, it is never the "right" time with him, and, it seems he is getting more angered, confused, hurt by the fact that he pretty much is kicked to the curb by his father, the father he thinks is his. I think its time, I just need advice. Do I tell just my son ? And, if I tell his siblings, what will they think of me? I have 2 kids I can talk to about anything, and 2 that are very critical of me, so, you see my dilemna. My son, thankfully is one of the kids that is pretty easy to talk to and loves me unconditionally. I want to tell him, but I want to do it right, and am not sure if we should involve his siblings,,,,will they feel the same about him, and all those worries I have. And no, I have no intentions of speaking with my ex about this first, last, or ever. He doesnt care, he's made it clear and for him, this will be a happy day as he won't have to be burdened by keeping what has now become, just my problem, and I quote him. And no, after 31 years, I do not know where the sperm donor father is, would be. That's the next concern, will my son be upset that I can offer him no info on his real father?
Advice? Please?
Thank you all

[AnnieBrooke]

Apparently below the law, if that is what he writes on his Facebook page.  I think your son would find it a bit of a relief (even if he is angry with you) to know.  It might help a lot of things fall into place.

[AnnieBrooke]

I hope someone will write in who has more direct experience in this kind of thing, but in my opinion I would tell your son but not his siblings, and let this be your son's call (whether to tell them or not).  Your ex-husband *did* legally adopt your son, so he is incorrect under the law to think he only has three kids, he has four.  However, it will help your son to understand why your ex has been such a jerk, and might help him (the son) clear up nagging feelings over what he may have sensed was true all along.

I assume your son would like to know more about his real father, just be prepared to tell him what you do know.

[Itstime31]

Thank  you. I think the same, let him decide who he wants to tell. I just hope this dosesnt make him feel more abandoned. Then again, its only my ex who has been a jerk to him.
I'm sure also he will have questions about his real father, I have no answers. I was 18, he was 19 we dated about a month and that was that, I can't even give him a last name. Yes, I am ashamed. I do appreciate your opinion very much though. Law? LOL, surely you jest, my ex is above the law! LOL,,,,,,,,he thinks.

[AnnieBrooke]

Apparently below the law, if that is what he writes on his Facebook page.  I think your son would find it a bit of a relief (even if he is angry with you) to know.  It might help a lot of things fall into place.

[allmymarbles]

By telling him the truth he will lose all guilt concerning his adoptive father. He will also see him as no one to be admired and will cease to want his love. Do him the favor. Tell him.