My Fair Duchess by Megan Frampton

The unexpected duchess…
Archibald Salisbury, son of a viscount, war hero, and proficient in the proper ways of aristocratic society, has received orders for his most challenging mission: Genevieve, Duchess of Blakesley. How she inherited a duchy isn’t his problem. Turning her into a perfect duchess is. But how can he keep his mind on business when her beauty entices him toward pleasure?

It was impossible, unprecedented…and undeniably true.
Genevieve is now a “duke”, or, rather, a duchess. So what is she to do when the ton eyes her every move, hoping she’ll make a mistake? Genevieve knows she has brains and has sometimes been told she has beauty, but, out of her depth, she calls on an expert. And what an expert, with shoulders broad enough to lean on, and a wit that matches her own. Archie is supposed to teach her to be a lady and run her estate, but what she really wants to do is unladylike—run into his arms.