[1] Katherine, twice widowed and aged about 42, was more than 20 years older than William, so the motive for the marriage was probably financial (her second husband, Henry, Lord Grey of Codnor, had left her much of his property).
As nephews of Edward IV the de la Pole family had a much stronger hereditary claim to the throne than Henry VII, who was descended through his mother from an illegitimate son of John of Gaunt.
[3] Even if William, unlike his brothers, had no personal ambition to seize the throne, his ancestry would have made it impossible for Henry to trust him.
The discovery of a plot involving the de la Pole brothers in 1501 sealed William's fate.
He was held prisoner in the Tower of London for 37 years till his death, longer than anyone else in the Tower's history, for allegedly plotting against King Henry VII with his brothers Edmund and Richard, who fled the country in 1501, after their conspiracy was detected.