I recently told my son he was only a half brother to his dad’s new child after he came home from a visit telling me about his new brother. I explained to him that as his step mother is not his mum, it makes him a half brother. My ex is now upset that I didn’t involve him in this decision as he feels I should of discussed it with him first and agreed together how he refers to his sibling. He’s 9 years old so I feel he will work out for himself he is only half brother eventually so why not make it clear now. Have I been unreasonable?