February 12, 1554
Lady Jane Grey is executed for treason
As King Edward VI lay dying at the age of 15, he nominated his first cousin, Lady Jane Grey, as his successor. However, the Third Succession Act would require his half sisters, Mary I or Elizabeth I, take the Crown instead.
Jane was imprisoned, sentenced to treason, and scheduled for execution but spared once. However, Mary I (known as Bloody Mary after her death for her seeming love of executions and burning people at the stake), had Jane beheaded simply for being nominated for Queen.
Jane had been a devout Protestant and Mary an overzealous Catholic, so she was likely martyred rather than a victim of politics. She was 16 or 17 at the time of her death.