The Royal Game by Linda Keir

American pop singer Jennie Jensen is ready to marry the love of her life, England's Prince Hugh, but someone is determined to keep her from becoming a princess—any way they can. To give her fairy tale a happy ending, she'll have to play the royal game.
Jennie Jensen is touring Europe, already living her dream, when Prince Hugh of Wales—the future King of England—appears at a gig and requests his favorite song. He's already smitten, and soon so is she. After a secretive, whirlwind romance, Hugh proposes, and when Jennie accepts, her world changes overnight. She's still learning to navigate the minefield of constant scrutiny, barbed social interactions, and royal protocol (there are rules about pantyhose), as she learns that not everyone in England is excited about the prospect of an American princess.
When Jennie receives a threatening note, she can't help but see the parallels between herself and another young woman who struggled to adjust to royal life: Hugh's mother, Princess Penelope, who was killed in a mysterious plane crash. And as the threats to Jennie grow more serious, she digs into Penelope's past, discovering a woman who also suspected someone in the palace was out to get her. Was Penelope murdered? And is Jennie next? With the eyes of a nation on her as the royal wedding approaches, she's in a race against time to save her marriage ... and her own life.
Both a charming love story and a thrilling mystery, The Royal Game reveals one woman's determination to find happily ever after—on her own terms.