The King's Curse: Philippa Gregory

They trust her to watch the House of Tudor rise… Only she knows it will fall.
Heir to the Plantagenets, Margaret Pole, is a rival claimant to the Tudor throne. Buried in marriage to a loyal Tudor supporter, she becomes guardian to Arthur, the young Prince of Wales, and his beautiful bride, Katherine of Aragon.
But her destiny is not for a life in the shadows. Tragedy throws Margaret into poverty, yet the king's death restores her to a place at young Henry VIII's court, as a lady in waiting to Queen Katherine.
As the Tudor court sours, Margaret has to choose between her allegiance to the increasingly tyrannical King Henry, or to her friend, his abandoned queen. And Margaret is hiding a deadly secret… that a curse was cast on the Tudor line, and she is watching it come to pass.