Bridgerton The Duke and I Daphne's Story by Julia Quinn

Simon Basset, the irresistible Duke of Hastings, has hatched a plan to keep himself free from the town's marriage-minded society mothers. He pretends to be engaged to the lovely Daphne Bridgerton. After all, it isn't as if the brooding rogue has any real plans to marry - though there is something about the alluring Miss Bridgerton that sets Simon's heart beating a bit faster.

And as for Daphne, surely the clever debutante will attract some very worthy suitors now that it seems a duke has declared her desirable. But as Daphne waltzes across ballroom after ballroom with Simon, she soon forgets that their courtship is a complete sham. And now she has to do the impossible and keep herself from losing her heart and soul completely to the handsome hell-raiser who has sworn off marriage forever!