My DS1 was born after a short, inadvised "relationship" with someone who didn't want to know. When he was 1 year old I met my DH and we got married when DS1 was 3. My DH adopted him and all was well. My DS1 has always known this and has no interest in finding his "natural" unnatural father, he is now nearly 20. However, since we married my DH and I have had 4 other children, as it has never been an issue for my DH or my DS1 we have never told the others that they have a different father to their oldest brother. It genuinely never occurred to me to do so. Last time I spoke to DS! about it, he said that "Dad is his Dad and the others are his brothers and sisters and that's the end of it", but having a chat with DS2 recently, he was talking about one of his friends who has 2 half brothers, my DS2 was adamant that they weren't "real" brothers just half brothers and now I'm worried about he and the other kids will react when they find out that DS1 is "only" a half brother. Has anyone else been in this situation? Just for information, DS1 also has other h