One of the most disturbing was "The Favored Child" by Philippa Gregory, author of "The Other Boleyn Girl".
All goes smoothly for the first two-thirds of the book. Then, the heroine finds out that her late aunt, who died when she was too young to know her, and whom she has admired throughout the book, is not just her aunt - she was ALSO her biological mother. Then her creepy cousin/brother rapes her, kills her adoptive parents and manipulates her fiancé away from her. She winds up having a baby, leaving it with some Gypsies, and then dying.
Ick. What a sick book. It's part of a whole trilogy that's like that... but fortunately, I've never read the other two.