Fia still wanted to keep it a secret (she judge the Black Dragon power is still weaker than the Demon King's right-hand-man) and Quentin thought he didn't have permission to talk about it so he kept it a secret.
The 4th Captain, Quentin only told the 6th captain, Zakiria (the man who complained about 4-packs ABS and have the name similar to the Black Dragon) because they (4th and 6th Captain) would soon encounter 2 Blue Dragons and the Black Dragon must show his true form.
Quentin only told the 6th Captain to make him keep it a secret.
The Demon King General is still isn't reintroduced in the story yet.
This story is kind of straight forward so I think he will be the last boss or a reason (that Author used) to make Fia remain un-noticed.
Fia's reverse harem is on the way of being introduced soon.
1st member: Captain Cyril.
Fia will visit his hometown, Sutherland, soon and healed the scar of his heart soon (His parents hate him, his citizen hate him for being the son of the tyrant duke who killed his own people in angry)
2nd member: the 4th captain, Quentin. Or more like, he worships her.
3rd member: the 6th captain, Zakiria. He swore to protect her with his life, a Knight's Oath.
4th member: the 13th captain. Fia's past life, Princess Safirena's bodyguard. Or more like, he worships her as well.
5th, 6th, 7th members: Crown Prince, 2nd prince, and 3rd prince of another country, Red + Blue +Green.
They kept their names a secret with Fia so she called them by nicknames.
Fia cured them of the Curse of the Royal family.
They believe Fia is the True Goddess Reincarnation.
Fia is being friendly and hugs them like brothers but they all scream and tell her to behave like a girl while blushing.