Which Queen of England married her brother-in-law?

Catherine of Aragon (16 December 1485 – 7 January 1536) was Queen of England from June 1509 until May 1533 as the first wife of King Henry VIII.

The daughter of Isabella I of Castile and Ferdinand II of Aragon, Catherine was three years old when she was betrothed to Arthur, Prince of Wales, heir apparent to the English throne. They married in 1501, but Arthur died five months later. In 1507, she held the position of ambassador of the Aragonese Crown in England, the first female ambassador in European history. Catherine subsequently married Arthur's younger brother, the recently ascended Henry VIII, in 1509. For six months in 1513, she served as regent of England while Henry VIII was in France.

By 1525, Henry VIII was infatuated with Anne Boleyn and dissatisfied that his marriage to Catherine had produced no surviving sons, leaving their daughter, the future Mary I of England, as heir presumptive at a time when there was no established precedent for a woman on the throne. He sought to have their marriage annulled, setting in motion a chain of events that led to England's schism with the Catholic Church. When Pope Clement VII refused to annul the marriage, Henry defied him by assuming supremacy over religious matters. In 1533 their marriage was consequently declared invalid and Henry married Anne on the judgement of clergy in England, without reference to the Pope.