So there is a lot of theories concerning Arthur and Hook- the most popular that he is Hook’s father.
I think that Arthur is actually the child of Hook. More specifically, the child of Hook and Emma.
This would explain how Arthur becomes a king (child of a princess) even though Hook isn’t royal. Also, Camelot is an alternative universe that might be past, present, or future. This theory obviously imagines Camelot in the future where Hook and Emma’s baby becomes a king and rules like a hero because he has the blood of the savior and a captain, not to mention he’s the grandchild of Prince Charming and Snow White.