Conversation so far:
What was the Hellfire Club?
The Hellfire Club is a fictional society appearing in American comic books published by Marvel Comics.
Why was Sage sent to spy on the Hellfire Club?
Sage is sent to spy on the Hellfire Club as Tessa, and to keep watch on Sebastian Shaw.
Why was Charles Xavier recruiting X-Men?
To both shelter and train mutants from around the world, he runs a private school in the X-Mansion in Salem Center, located in Westchester County, New York.
Was Charles Xavier successful at recruiting X-Men?
Why was Tessa remorseful about the Hellfire Club?
Tessa is remorseful that she is unable to prevent the corruption of Phoenix into the Black Queen.

Question: So she created Dark Phoenix?
Self-contained rewrite: So Tessa created Dark Phoenix?