Answer by taking a quote from the following article:

Elizabeth of York (11 February 1466 - 11 February 1503) was queen consort of England from 1486 until her death. As the wife of Henry VII, she was the first Tudor queen. She was the daughter of Edward IV and niece of Richard III, and she married the king following Henry's victory at the Battle of Bosworth which started the last phase of the Wars of the Roses. She was the mother of King Henry VIII.

Elizabeth's mother made an alliance with Lady Margaret Beaufort, mother of Henry Tudor, later King Henry VII, who had the closest claim to the throne of those in the Lancastrian party. Although Henry Tudor was descended from King Edward III, his claim to the throne was weak, due to an act of parliament passed during the reign of Richard II in the 1390s, that barred accession to the throne to any heirs of the legitimised offspring of Henry's great-great-grandparents, John of Gaunt and Katherine Swynford. Despite this, his mother and Elizabeth Woodville agreed Henry should move to claim the throne and, once he had taken it, marry Elizabeth of York to unite the two rival houses. In December 1483, in the cathedral in Rennes, Henry Tudor swore an oath promising to marry her and began planning an invasion.  In 1484, Elizabeth of York and her sisters left Westminster Abbey and returned to court when Elizabeth Woodville was reconciled with Richard III, which may suggest that Elizabeth Woodville believed Richard III to be innocent of any possible role in the murder of her two sons (although this is unlikely owing to her involvement in Henry Tudor's failed invasion of October 1483). It was rumoured that Richard III intended to marry Elizabeth of York because his wife, Anne Neville, was dying and they had no surviving children. The Crowland Chronicle claimed that Richard III was forced to deny this unsavoury rumour. Soon after Anne Neville's death, Richard III sent Elizabeth away from court to the castle of Sheriff Hutton and opened negotiations with King John II of Portugal to marry his sister, Joan, Princess of Portugal, and to have Elizabeth marry their cousin, the future King Manuel I of Portugal.  On 7 August 1485, Henry Tudor and his army landed in Wales and began marching inland. On 22 August 1485, Henry Tudor and Richard III fought the Battle of Bosworth Field. Richard III, despite having the larger army, was betrayed by one of his most powerful retainers, William Stanley, and died in battle. Henry Tudor took the crown by right of conquest as Henry VII.

Who is Richard III?
In 1484, Elizabeth of York and her sisters left Westminster Abbey and returned to court when Elizabeth Woodville was reconciled with Richard III,