Devil's Kin — Anne Herries

To escape the unwelcome advances of her stepfather, Hester Stanley runs away to become mistress of a man she hardly knows.

Posing as brother and sister in pre-revolution Paris, Hester is blissfully happy with Beau Vane -- until doubts begin to emerge... Why does Beau claim to be the Devil's brother? And, above all, why will he not marry her?

Angry misunderstandings turn to bitter quarrels and Hester returns to England to marry her faithful admirer Tony Marchant. But the child she bears is Beau's, so how can she ever learn to forget the man to whom she has given her heart?