Remember back in Act One, Scene Four of Richard the Third, when George Duke of Clarence retells his nightmare, which begins
Methinks that I had broken from the Tower
And was embarked to cross to Burgundy
— I.iv.9-10
One has to wonder if this is a reference to an entire sequence of historical events NOT discussed by Shakespeare…
In 1476–five years after the Battle of Tewkesbury–George Duke of Clarence became a widower. His wife, Isabella Neville–remember, she was the older daughter of Warwick “the Kingmaker”–died at the age of 25, after bearing two children to Clarence, Margaret in 1473, and Edward in 1475 (these two being the children referenced in the play).
A year after Isabella’s death, Charles the Bold of Burgundy died in battle. Clarence’s sister Margaret had been Charles’ third wife (married off to him by Edward IV in 1468, exacerbating Edward’s relationship with the aforementioned Warwick), but she delivered to him no heir. The only heir Charles did have was a twenty year-old daughter from a previous marriage, Mary of Burgundy.
The widowed Clarence, seeking both a new wife as well as a political alliance with Burgundy, made known his intention to seek the hand of Mary. His brother and king, Edward, however, forbade the match.
Within months, George Duke of Clarence is found guilty of treason, and imprisoned in the Tower of London on January 16. By February 7, he has been sentenced to death. And he is then “privately executed” on February 18.
Throughout his political life, Clarence seemed more likely than Richard to betray his brother Edward in hopes of landing the throne (in fact, he did in joining Warwick’s rebellion). Could Clarence’s execution be less of a trumped-up charge executed in haste at the secret order of Richard, and more of a legal punishment for treason? Absolutely… but that wouldn’t suit Shakespeare’s propagandistic purposes, now would it?