She married. O, most wicked speed, to post
With such dexterity to incestuous sheets!
It is not, nor it cannot come to good.
But break, my heart, for I must hold my tongue.

– William Shakespeare

Hamlet, Act 1, Scene 2. Hamlet is not only disgusted with his mother’s remarriage after his father’s death, but also the fact that she committed "incest" by wedding his father’s brother. In Shakespearean times such a marriage of close relatives would have been regarded as incest.