The Day of the Duchess: Scandal & Scoundrel, Book III (Scandal & Scoundrel 3) / Sarah MacLean

Malcolm Bevingstoke, Duke of Haven, has lived the last three years in self-imposed solitude, paying the price for a mistake he can never reverse and a love he lost forever. The dukedom does not wait, however, and Haven requires an heir, which means he must find himself a wife by summer's end. There is only one problem--he already has one.
 

After years in exile, Seraphina, Duchess of Haven, returns to London with a single goal--to reclaim the life she left and find happiness, unencumbered by the man who broke her heart. Haven offers her a deal; Sera can have her freedom, just as soon as she finds her replacement...which requires her to spend the summer in close quarters with the husband she does not want, but somehow cannot resist. 

The duke has a single summer to woo his wife and convince her that, despite their broken past, he can give her forever, making every day...