A Secret Affair — Mary Balogh

Born a commoner, Hannah Reid has been Duchess of Dunbarton since she was nineteen years old. Now her husband is dead and, more beautiful than ever at thirty, Hannah has her freedom at last: To the shock of a conventional friend, she announces her intention to take a lover -- and not just any lover, but the most dangerous and delicious man in all of upper-class England: Constantine Huxtable. Constantine's illegitimacy has denied him the title of earl, so now he denies himself nothing. Rumored to be living the easy life of a sensualist on his country estate, he always chooses recent widows for his short-lived affairs. Hannah will fit the bill nicely. But once these two passionate and scandalous figures find each other, they discover that it isn't so easy to extricate oneself from the fires of desire -- without getting singed.