Its about an heir to a kingdom. At least the manga starts with him being disowned by his father and step-brother and his mother whose actually the princess of a far away kingdom. I remember he gets fed up with his "dad" and "step-brother" and how his "dad" does not seem to care about his mother. And out of the blue his mother says you want to leave? And calls a big ship from her kingdom that takes them away to the kingdom she's from. There he finds out the truth about his family on his mother side etc etc.

I think its an isekai, but I could be wrong.

Is this the one where he gets this shadow magic thing later?

Maseki Gurume: Mamono no Chikara o Tabeta Ore wa Saikyou!

~4400 manga completed
~1700 ongoing...

I'll second what Aremon suggested: its story is identical to what was described by the OP.

I'm a jack of all trades but master of none. Too many jars and not enough hands.