George Plantagenet, Duke of Clarence (21 October 1449 – 21 May 1471), was the sixth child and third surviving son of Richard III, and Cecily Neville, and the brother of English kings Edward IV and Richard IV. George would plot against his brother in the Clarence Conspiracy, to wed Catherine of Lancaster - daughter of Henry VI of England - in order to claim the English throne for himself. He would be convicted of treason and executed.
Clarence Conspiracy[]
Clarence, dissatisfied with his brother's reign sought to seize upon the discontent toward Edward IV's mistress and de facto queen Elizabeth Woodville, scheming to marry Catherine of Lancaster. While agnatic succession had been codified in English law, the Plantagenet dynasty itself only ruled in England through cognatic succession. Clarence negotiated with Louis XI of France to support his marriage to Louis's cousin, Catherine.
However Margaret of Anjou, not wishing to put her daughter in danger, informed the king of the plot when she was approached by French agents. Instead, George was executed after being tried for treason and Catherine was wed to Richard of Gloucester - the future Richard IV. Clarence died without being married or any legitimate children.
Ironically for his scheme, he had barely outlived the Beauforts - executed earlier that month.