From The Wall Street Journal:
Margaret Beaufort was never queen, even uncrowned, but her only child became Henry VII when he defeated Richard III at Bosworth Field in 1485, and Nicola Tallis, a British scholar and the author of a book on Lady Jane Grey, may reasonably style Margaret the mother of the Tudor dynasty. Margaret was married to Edmund Tudor when she was only 12. She was both a mother and a widow at 13.
Margaret’s own lineage was more distinguished than her husband’s. The Tudors were minor Welsh nobles, but she was descended from John of Gaunt (Shakespeare’s “time-honoured Lancaster”), the third son of Edward III. In “Uncrowned Queen,” Ms. Tallis makes much of Margaret’s “royal blood,” but it was tainted, for Gaunt had several illegitimate children by a mistress, each surnamed “Beaufort.”He did at last marry their mother, after his wife’s death, and they were legitimized thereby, but they were also, by some accounts, barred from the royal succession. Henry VII would win the crown by conquest; his hereditary right was dubious.
Margaret had two husbands after Edmund Tudor: a duke’s son and an earl. Both matches were prudent; she needed a husband to protect her extensive property during the War of the Roses, when the houses of York and Lancaster vied for the English throne. Ms. Tallis insists that the marriages were successful in other ways, too, even affectionate.
. . . .
Margaret was now engaged in plotting rebellion—and the return of her son. It is clear that she was an active conspirator, and one can only wonder at Richard’s continued tolerance of her. Henry’s invasion followed, and the decisive moment at Bosworth came when Margaret’s husband, Thomas Stanley, Earl of Derby, switched sides and secured his stepson’s victory.
Link to the rest at The Wall Street Journal (Sorry if you encounter a paywall)