Am I revealing things too soon?

I'm having second thoughts about a scene in Winter's Queen, wherein the MC has a talk with the Winter King about her upcoming marriage to the King's son and why it's a bad idea. She basically lays the villainous prince's plan (patricide following the wedding so the prince can seize the throne) bare, but the King dismisses her concerns as foolish. This comes back to bite him in the butt when things play out almost as the MC predicted, resulting in the King being nearly killed by his son after the wedding plan goes sour.

This exchange takes place in chapter 8 of a (currently) 21-chapter book. Originally I didn't have the MC fully realize the prince's plot until almost the climax of the book, in chapter 16. It was meant to be a big twist, but at the advice of my beta reader I decided to experiment with showing my hand earlier. As I said, though, I'm not sure which is the better course of action. Here's the ch. 8 conversation (or at least the most relevant excerpt) for context's sake:


“His Highness seems to value your opinion highly,” [Ariel] said at last. The glee in Fiachra’s face during their first meeting with the King had been all but palpable.

“He always has. As any heir should value the opinion of the one he seeks to inherit from. How else is he to follow the path I trod before him?”

“Indeed, Majesty.” Ariel shuddered inwardly to think of what Fiachra would be like as king. His ego didn’t need any more inflating. “But I can’t help but think maybe he means to speed the process along, and... clear the path ahead of him.”

The King looked at her sharply. “What do you mean?”

She took a deep breath. “Does it not strike Your Majesty as suspicious that His Highness wants to get married so badly, as you yourself mentioned before? It also sounds like he really wants an heir of his own, given he went to so much trouble to find a human bride rather than having his pick of eligible Fae. And it goes without saying that you’re immortal, and thus can’t give over the throne by dying of sheer old age. Likewise you seem to be in excellent health and well-liked by your subjects, so I can’t think of any reason you would choose to abdicate. What other option is there for him, if His Highness seeks the throne for himself?”

His eyes narrowed. “You seem very certain of this for a girl who has known my son little less than two days. Has he told you outright that he seeks kingship?”

“No, Your Majesty. But I think it would be wise not to dismiss the possibility.”

He raised a brow. “I think you have put too much stock in fairy-tale conventions.”

The King’s words were so ironic, Ariel wondered if they hurt him. “Those conventions have their roots in truth, Your Majesty, and they persist in story after story for good reason.”

“Even so, why would my son seek to kill me?”

“You said yourself that he seeks your approval. I saw how happy he was when you approved his choice to marry me--”

“As did I. So he should be satisfied.”

Ariel bit her tongue to keep from saying out loud that one moment of satisfaction was probably just a lot more incentive for Fiachra to act. How many times before now had he been denied his father’s praise?

 

I'm very much undecided. I feel like having Ariel figure things out earlier gives her a little more incentive to leave, because she knows exactly what's at stake for her (or at least assumes she does). But at the same time, I'm worried that it makes my plot seem bland and predictable, if the reader knows what's coming.