Both Boleyn sisters in The Other Boleyn Girl have relationships with Henry VIII.
The sisters are Mary Boleyn and Anne Boleyn, members of an ambitious Tudor-era family. In Philippa Gregory's historical novel and its film adaptations, Mary becomes Henry's mistress first. Her relationship with the king brings the Boleyn family influence at court and results in children who were widely believed to be Henry's, although their paternity was never formally acknowledged.
Anne later attracts Henry's attention and refuses to remain merely his mistress. Their relationship becomes central to the story because Henry seeks to end his marriage to Catherine of Aragon and marry Anne. The resulting political and religious crisis eventually contributes to England's break with papal authority and the formation of the Church of England.
The story is historical fiction, so its dramatic details should not be treated as fully documented fact. Historians generally accept that Mary Boleyn was Henry's mistress and that Anne became his partner and queen, but the timing and details of Mary's affair are less certain. Anne married Henry in 1533 and was executed in 1536 after their relationship collapsed.