It’s All About the Duke by Amelia Grey

Nearing thirty, the Duke of Rathburne is finally ready to make amends for the wager that caused him and his best friends such scandal―but taking on a ward who needs a husband is a feat he’s not sure he can manage. The last he saw of Miss Marlena Fast, she was a spirited little ruffian, not the sort of bride most bachelors on the marriage mart sought. But one glance at the lovely lady she has become is enough to convince him otherwise…

Orphaned young and shuffled from family to family, Marlena counts on her fierce independence and quick wits to keep herself content. Being the responsibility of a notoriously wicked duke who upended so many lives is an unexpected challenge when she realizes he arouses her decidedly feminine desires. Marlena must be careful. She has her own scandalous secret to protect. If he finds out, will it shatter her chances of a happily-ever-after with the notorious rake?