Mary had been unhappy with her marriage of state to Louis, as at this time she was almost certainly already in love with Charles Brandon, 1st Duke of Suffolk. Henry knew of his sister's feelings but wanted any future marriage to be to his advantage. When he sent Brandon to bring Mary back to England in late January 1515 he made the Duke promise that he would not propose to her. However, the couple married in secret in France on 3 March 1515. Technically this was treason, as Brandon had married a Royal Princess without Henry's consent. The King was outraged, and the Privy Council urged that Brandon should be imprisoned or executed. Because of the intervention of Thomas Wolsey, and Henry's affection for both his sister and Brandon, the couple were let off with a heavy fine. They were officially married on 13 May 1515 at Greenwich Palace.
Mary was Brandon's third wife, and he had two daughters, Anne and Mary by his second marriage to Anne Browne. She had died in 1511. Mary would raise the girls alongside her own children. Even after her second marriage, Mary was normally referred to at the English Court as "the French Queen," and was not known as "the Duchess of Suffolk" in her lifetime, despite being legally allowed to be. Mary spent most of her time at the Duke's country seat of Westhorpe Hall in Suffolk.
Relations between Henry VIII and Mary were strained in the late 1520s when she opposed the King's attempt to obtain an annulment of his marriage to Katherine of Aragon, whom Mary had known for many years, and developed a strong dislike for Anne Boleyn, whom she had first encountered in France.