The Purest of Diamonds?

Leila has always lived modestly in the shadows of her two older, extroverted sisters. Then one day she meets a man named Raffa, the Duke of Cantalabria and an infamous playboy. They quickly become close and end up sleeping together. Leila is delighted by the love she has found, but when she finds out she’s pregnant, she realizes that she doesn’t know anything about Raffa at all! Source: Harlequin