How do I (45 f) tell my son (19 m) the real reason my sister gave him up and wants nothing to do with him was because of racism?

Hi this is really playing on my mind. I would appreciate any suggestion. My husband suggested to post here. I came from a racist family. I was always the black sheep in my family because I just didn't buy into there racist bs. I was always getting in trouble for making friends outside my race. I got disowned for dating my now husband.

For 5 year's I had no contact with my family when my sister 40 showed up at my house. She was very upset. Apparently she went to a party and got drunk and got pregnant to a guy of a different race. She was deathly afraid of our parent's reaction. Me and my husband took her in. She lied to our parent's and said she found a job in my city and living with friends. She didn't want to abort my son. She did struggle with being around my husband in the beginning and made some comments and I told her if she kept that up she can go back to our parent's because I wasn't going to tolerate her racism. She was desperate enough to accept that she would have to be nice to my husband. So she kept her distance and comments to herself.

I was with her when she gave birth to my son. It was obvious he was mixed. She didn't even want to hold or feed him. She was withdrawn and detached from him. She then outright told me that she didn't want him and that she wished she had aborted him and called him a racist slur. I remember being stunned and speechless, who can say that about an beautiful innocent baby. I remember going home upset and my husband asked what's wrong. I told him and he was quite and then the next day he asked me if we should adopt him so that at least he was connected to actual family. I wanted that as well. So I went to the hostpital and asked my sister if I could have him. I 100% thought she was going to turn me down. But she just said okay on the condition that I make sure our parent's never find out and that he never knows about her. I agreed. Me and my husband officially adopted our son. Afterwards she left and I haven't seen or heard from her since.

Obviously my son knows me and my husband are not his biological parent's. He himself at age 12 asked why he didn't look like us and we sat him down and told him the half truth. My son is sensitive and I didn't want hurt him by telling him the whole truth. He accepted it. He also knew I wasn't in contact with my family due to racism and I was hoping he would get the hint as he grew older. He didn't. Naive of me. Which brings us to 5 days ago. My son announced he wanted to talk to my sister. He said he wanted know about his biological father. He asked for her information and I told him I can't give him that. He asked why and I said it's not a good idea. He got upset and said he had a right to know. I started crying because all I could picture in my head was sister calling him a racist slur when he was a baby. He left and my husband came home early from work because my son also got upset with him as well. He said its probably time to tell him the whole truth. I didn't want too. I don't want to hurt my son. My husband said he understood being his mother I wanted to protect him but it's the right thing to do. But now we are struggling on HOW we should tell him. Please does anyone has any suggestions please?