"'My bright twin sister of the sky': Manfred, Moore's Loves of the Angels, and the Shadow of Augusta Leigh" establishes that the angelic protagonist of Thomas Moore's "Second Angel's Story" (the second of the three verse tales comprising his 1821 The Loves of the Angels) was meant to represent Lord Byron, and argues that the tale is an allegory of Byron's fall from grace through his incestuous love for his half-sister Augusta Leigh.  My article reveals a forgotten friendship between Moore and the nineteenth-century writer Robert Balmanno, and demonstrates that Balmanno's wife Mary, an editor of Moore's works, knew that Moore had intended the angel Rubi to represent Byron.  I correct the dating of a crucial 1814 letter from Moore to Byron on the subject of Augusta that had previously been thought to date from Byron's 1816 marriage crisis, and on the evidence of this letter and others, including a significant postscript that Moore censored in his biography of Byron, I demonstrate Moore's almost certain pre-1817 knowledge of Byron's incest.  Speculating about when and how Byron was likely to have revealed his secret to Moore and about Moore's probable reaction to Byron's 1817 incest-drama Manfred, I analyze the "Second Angel's Story" as the veiled musings of Byron's appointed biographer upon a chapter of Byron's life about which he would otherwise have to remain forever silent.

Note: Due to a problem with the printing process, this article contains a number of errata that were beyond my control.