Anyone have experience of adult children being upset about their father having a new baby?

[Moomin8]

I'm due to give birth to a baby girl next month. My partners son has said he doesn't want anything to do with the baby. Apparently he still hasn't got over his parents break up which happened 4 years ago. His mum has moved her new partner into the house He's 22 and has been angry about it from the beginning. He won't even spend any time with me.

Anyone have any experience of this sort of thing? My children are fine with it all, in fact they can't wait to meet their new sister. They are 18, 15 and 10.

[Marinetta]

My partner was 33 when his dad had a baby with his second wife. He wasn't particularly happy about the marriage anyway but them having a baby absolutely horrified him. He is one of 4 and the second wife also has 2 children of her own so he had convinced himself that they wouldn't want any children together then when it happened it was a massive shock. He has met the baby once but probably won't be going again. He has his own life now and our own child who is older than his new sister and he feels very disconnected from the whole thing