“Princess,” she says, when all the others are gone to deal with Discord, “what is Hell?”
It’s arguably unwise to act in any way on anything Discord says, but if this question is going to lead where she expects it to lead, they would have gotten there anyway.
Celestia looks, for a moment, older and more tired than Valiant Victory has seen her in a long time. (Well, she hasn’t seen anything in a long time, sidereal, but it had been a rare look even when the war was at its worst.) “The universe is very large, my little—”
“Don’t call me that,” says Valiant Victory, and then, “Does it have anything to do with the incident in the ballroom earlier?” She hadn’t personally been at the Gala to witness it, but it would have been hard not to hear of the vision of horror inflicted on the guests by the strange, visibly (to her) evil mare who had unpetrified her, a pony who was apparently, in spite of all this, friendly with the new Bearers of the Elements of Harmony and permitted in Celestia’s throne room—that isn’t, actually, the important part—
She notices that she is, actually, hesitating to ask her next question, because she’s still just a pony, and she wants to live just a moment longer in the world where the answer isn’t ‘yes’. She stops, because the people in Hell, if they’re real, don’t have that option.
“Was that vision of a place that actually exists?”
“Yes.”
She shows no outward sign as the last of her innocence crumbles to dust. “How long have you known?”
“Always.”
She is slow to anger—she has to be—but that, actually, will do it.