It's In The Duke's Kiss: A Danby Regency Novella
Julie Johnstone
Lucian, the Duke of Blackbourne, is tired of playing keeper to his irresponsible brother. He vows to quit, but when his brother resolves to seduce the impetuous Lady Emmaline, Lucian knows he must save his foolish brother and the innocent debutante from themselves. Yet his plan to intercede goes awry when he finds himself drawn to the woman who is everything he was positive he didn’t want in a wife.
But his brother won’t give up so easily, and soon Lucian’s well-intentioned plans are revealed. Now to keep Lady Emmaline’s heart he must prove that he’s truly not the stuffy, sneaky duke he seems to be.