In 1478 Richard's brother, Edward IV, had the middle of the three brothers, the Duke of Clarence, executed for treason.
He was buried in Tewkesbury Abbey having been, it is said, drowned in a barrel of Malmsey wine. While Shakespeare's play blamed Richard for arranging it all, there is no evidence that he was involved. However, it did mean that Richard Duke of Gloucester was now third in line to the throne behind Edward's sons: Prince Edward and Prince Richard.
The Princes in the Tower
In 1483 a crisis came, Edward IV died. Now Prince Edward became Edward V, but he was only twelve years old and vulnerable.

His uncle Richard rushed south to take charge of the young King as 'Lord Protector.' According to one chronicler he was mindful that the previous Duke of Gloucester had done the same for Henry VI sixty years before. The events that followed are controversial.
Edward's coronation had been planned for 4th May, but that was the day Richard and Edward arrived in London, so it was postponed until 22nd June. While preparations for the ceremony were being made, Richard revealed that a plot had been found against him. A round of arrests of Richard's rivals followed. When the 22nd of June arrived, Edward was not crowned, instead a churchmen revealed to the people of London that he believed Edward's father had married illegally making Edward illegitimate and barring him from the throne. At this news petitions were raised that Richard be King. Within four days Richard Duke of Gloucester was recognised as Richard III 'by the concord assent of the Lords and Commons'.
As for the boy who had been Edward V and his brother Prince Richard, they were sent to the Royal apartments in the Tower of London. After some weeks they were never seen or heard of again. What happened to them has intrigued historians ever since.
Illustration: Document signed by Edward V 'Edwardus Quintus', Richard 'Loyaulte me lie (Loyalty binds me) Richard Gloucestre' and the Duke of Buckingham 'Souvente me Souvene (Often I remember) Harre Bokyngham'. May or June 1483 © The British Library Board,Cotton MS Vespasian F xiii