Lexicon: HBP Mystery Person Revealed?

The Lexicon has received information that may reveal the identity of someone mentioned at the end of HBP via initials. (For the unspoiled, we’ll refrain from posting them.) It should be noted that this, while it comes from a reliable source, is still rumor until confirmed or denied by Jo & Co. It is, however, strong enough of a rumor to bring to your attention.