2006, Aaron Schwabach, "Harry Potter and the Unforgivable Curses: Norm-formation, Inconsistency, and the Rule of Law in the Wizarding World", Roger Wiliams University Law Review, Volume 11, Issue 2, Winter 2006, page 310:
In addition to traditional commentary, the sites contain filk, fanfic, slash, and other derivative works, including a genre that has provided the English language's worst recent new word and concept, Weasleycest.
Unlike Weasleycest, which has spread across the fandom like kudzu, Malfoycest has always been more difficult to find, and its writers a bit more secretive.
2008, Jenny Alexander, "Tortured Heroes: The Story of Ouch! Fan Fiction and Sadomasochism", in Sex, Violence and the Body: The Erotics of Wounding (ed. V. Burr & J. Hearn), "weasleycest" page 121:
Weasleycest is devoted to stories containing Weasley family (sibling to sibling) incestuous pairings. The first member of the Weasleycest LJ community was Lady Feylene (in 2003) […]
2010, Leila Green, The Internet: An Introduction to New Media, Berg (2010), →ISBN, page 149:
Adult-content HP fan fiction includes a range of specialist pairings such as Twincest: incest between one of the sets of HP twins; or Weasleycest: incest within the Weasley family.
Although, in Weasleycest, incestuous stories with all members and possible pairings engaging in sexual acts can be found, the most popular pairing by far is George and his twin Fred.
2012, "Family Relationships in Fanfic [Keeping It in the Family]", Wincon 2012 programme, page 21:
And if you just want to come reminisce about the glory days of Weasleycest and your early exposure to Flowers in the Attic, that’s fine too!