Magneto revealed as father of Quicksilver and the Scarlet Witch via the appearance of Magda in X-Men #125. The origin of Quicksilver and the Scarlet Witch storyline discussed in detail by Mark Gruenwald in the letters page of Avengers #192. This information added 2005 by Steven Tice.
Letters on The Avengers #182. Letters from Mike Labrie, Bill Krauss, and Larry Brundin.