Someone needs to write a story with Danny being Bruce's son.
Everyone is like do we tell him( Damien)
They think will go all murdery on Danny.
Only he knows about his older brother or half brother. ( Writers pick)
They hide all the normal weapons and the like then tell him. Tell him Danny doesn't have any ties to the hero world and want to keep it that way.
They don't know about phantom ( the worlds first hero)
A few months later the Ghost King is needed. Only no one knows a safe way to summon him.
Damien goes I got this, some low rate magic user mocks him. And when Danny shows up the mocking dies down.
Danny is all edlrich horror and is like are you picking on my baby brother?
Once that is handled they ask him for help.
This is how Batman finds out his oldest blood son is a hero but also a ghost hero.
Danny turns to Damien and is like you know she could have handled this.
Damien is like yes she could have but you talked to her last week and know it's fashion week or something big in fashion. ( I don't know these things).
Once the trouble is dealt with and Damien asks if he wants to see his room. Not Damien but Danny's room Damien had ready for him and to meet Afried.
Danny is like sure, over dinner someone asks who they where talking about. The person that could have handled what Danny was summoned for.
They both go oh our sister. She is a hero in Paris has a team and everything.
And that is how Bruce learns about his daughter.