A royal bastard is a child of a reigning monarch born out of wedlock. The king might have a child with a mistress, or the legitimacy of a marriage might be questioned for reasons concerning succession.
Henry Fitzroy was the illegitimate son of King Henry VIII by teenage mistress Elizabeth Blount.
Droit du seigneur, also known as jus primae noctis or prima nocta, was a supposed legal right in medieval Europe, allowing feudal lords to have sexual relations with any female subject, particularly on her wedding night.
Vasily Polenov: Le droit du Seigneur (1874); artist's interpretation of an old man bringing his young daughters to their feudal lord
Voltaire, who in 1762 was the first person to use the term droit du seigneur
Hector Boece, the first historian to record the droit du seigneur, in 1527
Image: Jules Arsene Garnier Le Droit Du Seigneur