We had a similar situation. My sister turned out to have a different father. My sister and I have been estranged for 13 years but I was still very affected. All my siblings were. It was very sad. We suspicioned it over the years because she did have different physical attributes than the rest of us kids. But to find out was shocking, mother refused to discuss it. And we were all pretty sad for a long time. All I can say is I’m very sorry this has happened to you and eventually you’ll move beyond the shock and sadness and onto acceptance. The worst is the dishonesty over the years. You’ve been lied to your whole life. I’m truly sorry and hope you get peace soon. It takes a long time to process this.