The book currently set as my profile has exactly that premise. He's a Wehrmacht soldier, she's an SOE agent but he obviously doesn't know it, he thinks she's just a simple French girl. He falls in love with her but in trying to impress her he behaves as a pompous prick and she can't stand him. But bit by bit he reveals a deeper side to himself and comes across as a man with depth and feeling and -- well. She does overcome her dislike, but only after a lot of soul searching.