Pseudoincest

Half of the cases were the classical father-daughter incest, a quarter of them the stepfather-stepdaughter pseudoincest and the remainder were abuse by relatives or siblings.

Source: wiktionary

Whether fact or fiction, Antiochus and Stratonice is a good story. […] At the core of the story lay the disturbing assertion that a father had passed his wife to his son. This pseudoincest plot toyed with cultural taboos of the Persian East and the Greco-Roman West, anticipating Sigmund Freud's later naming of the Oedipus complex as an unconscious sexual desire.

Source: wiktionary

The streets of the industrial cities of that time were teeming with street urchins, and the hideous class system of the British had arrived at its most impervious and solidified condition. The induction into a middle-class family of a street orphan would have been an extraordinary act at that time. This extraordinary act—while not completely unthinkable—becomes explicable if Earnshaw’s compassion is underscored by culpability. The spectral suggestion that Heathcliff was Earnshaw's illegitimate child won't go away. What is unthinkable is that this never occurred to Emily Brontë. The implication is a structural ghost that twists and shapes the subsequent narrative. We are not dealing with pseudoincest at all, but incest in all its colors.

Source: wiktionary

(Moore explains, for instance, that in 2015, pseudoincest porn was a popular genre.)

Source: wiktionary