A sequel of sorts to device heretic's Just Words, because I was dissatisfied with the ending, even if it was sort of poetic justice.

To Summarize:
Twilight finds out that she's adopted, from her brother, while he's drunk. Hurt, she goes to her parents; when they admit the truth of the matter she runs off to see Celestia. After a long talk, Celestia emphasizes the value of one's chosen family (or those that chose to be their family), placing that head of the value of biological relations.
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A week later, Celestia struggles with herself; For the first time in years, she really wants to tell Twilight and thinks she deserves to know. Nevertheless, the situation weighs heavily on her. Her past, the possibility of political fallout and disgrace, and Twilight's potential reaction to her callous dismissal of the value of biological relations weigh heavily on her. Still, if Twilight dies, never having known, it would be a crushing blow and an undeserved slight to her former lover.