Beneath the Silver Tide. SIlver tide, #1

Princess Elara has spent her entire life hiding a dangerous secret. She is the last of the Selkyn-a forgotten people who can shed their sealskin and become creatures of the sea. Forced into an arranged marriage with Prince Aldric of Ashmoor to unite two kingdoms, Elara enters a castle where duty comes before love. Her husband is distant, consumed by the weight of the crown, leaving her to navigate a lonely life among strangers.
The only person who truly sees her is Rowan, Aldric's younger brother. What begins as an unexpected friendship grows into a forbidden love that neither of them ever intended. As guilt, loyalty, and longing threaten to tear the royal family apart, an ancient enemy awakens beneath the waves. When Elara's sacred sealskin is stolen, she discovers that the stories told by kings are built on lies. Hidden beneath the sea lies the lost kingdom of Nerath, where the feared Deepborn have spent a thousand years guarding a darkness known as the Hollow Tide.
To prevent an ancient evil from escaping its prison, Elara, Aldric, and Rowan must set aside betrayal and heartbreak to restore the forgotten Wards that once kept the world in balance. But every truth uncovered comes with a greater cost. Every Ward restored brings them closer to a kingdom erased from history. And every step toward salvation draws the Hollow Tide closer to freedom. Filled with forbidden romance, ancient magic, breathtaking underwater kingdoms, and impossible choices, Beneath the Silver Tide is the sweeping first novel in an epic fantasy romance series about love, sacrifice, and discovering that the greatest legends are often the ones history tried to erase.