I remember reading Mario Vargas Llosa's, "In Praise of the Stepmother," about a young teen boy and his stepmother. A literay erotic novel - just don't get caught reading it at your local coffee shop. The author has a hang up with older women. In an early novel, Aunt Julia and the Scriptwiter, he delves into the affair between a radio soap opera writer and his divorced aunt. It's autobiographical.

http://www.nerve.com/Regulars/JacksNaughtyBits/Llosa/

That borderline incest trope is pretty popular.

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