Tou ni Torawareta Ningyo Hime

One day, Josephine, living on a Greek island, rescued a man who had fallen off his yacht. He had lost his memory, but his charming appearance and frank manner made Josephine fall in love with him. She offered her virginity and dreamed of a happy future, but her thoughts soon turned to despair. He, Alexander, was the crown prince of the kingdom of Aargau. In addition, he had a wedding coming up in a few weeks. She had no way to stop Alexander from regaining his memory, and just as she was about to break off her feelings for him, she realized that she was pregnant...! Source: Harlequin