1. Paraphrased from the Encyclopedia Britannica CD 98:

Buckingham played an important political role during the reign of Henry VIII.  As Lord High Constable, he bore the crown at Henry's coronation (23 Jun 1509).  The following November he became a privy councillor.  As a descendant of Edward III and with his offices, he was one of the most powerful men in England and was at one time considered a possible successor to the crown.  His power made him an object of suspicion to Henry and, especially, to Cardinal Wolsey.  He was ultimately accused of treason, probably falsely, for "having heeded prophesies of the king's death and his own accession to the throne and having voiced intentions to kill the king."  He was taken to the Tower of London and tried in the spring of 1521, where Henry VIII himself questioned witnesses and the accused.  Buckingham was executed that May on Tower Hill.  Buckingham is a prominent figure in Shakespeare's play, Henry VIII.

2.  Directory of Royal Genealogical Data [link died] by Brian C. Tompsett.