Queen of Hearts by Tracy Cooper-Posey

In America, she met an Indian called River.

Sadie travelled to America when she was nineteen, leaving behind her great family, to learn more about her real parents and how they died. While traveling in the Columbia River territories, her party is attacked by Indians and saved by a different tribe. Among them is the brave she comes to know as River.
Sadie learns that not only is River an Englishman, he is the son of the Duke of Caldwell. When his family learns he survived his parents’ death when he was an infant, River faces a choice: Leave Sadie and his tribe behind, or let the people of Caldwell suffer at the hands of his indifferent and selfish uncle…

This book is the thirteenth and final book in the Scandalous Scions series, bringing together the members of three great families, to love and play under the gaze of the Victorian era’s moralistic, straight-laced society.