Not quite apropos to the OP but several posts haven’t been: illegitimacy was more than just fooling around on a spouse or not being married when a child was born, and in fact the entire Tudor dynasty was illegitimate several ways.
They were descendants of Edward III through his son John of Gaunt, who had several illegitimate children with his mistress Kathryn Swinford (spellings vary). He married her when his second wife died, by which time their oldest son, John Beaufort, was an adult. He was legitimized by royal decree and papal bull (a favor by the king to his uncle, basically a pro forma by the Pope), but he was born and grew up illegitimate as his father was legally married to another woman.
John of Gaunt’s (legitimate) great nephew Henry V married Queen Catherine of Valois, the daughter of [the insane] King Charles VI of France. His early death left her a 20 year old widow with a baby [the insane] King Henry VI] who, like most royal babies, was raised by others and her mother rarely saw him. So, being a 20 year old widow in the English countryside, she not surprisingly began an affair with her [as we would call him today] bodyguard, a Welshman named Owen Tudor, and they had at least six children. Though Owen was single and Queen Dowager Catherine was a widow they were not free to remarry without the consent of the king (her infant son), and this was never given as Catherine died before he reached his majority, thus even though the Queen Dowager and Owen are believed to have had a wedding performed by a priest it was invalid and their children were all illegitimate. Owen was in fact imprisoned when the Queen died by his enemies at court, though his ‘stepson’ [technically his lover’s son] King Henry VI pardoned him as soon as he could and provided titles and revenues for Owen’s children with his mom, whom he completely regarded as his brothers and sisters but who were not legitimate. (Owen was later beheaded when captured, fighting on his stepson’s side, in the ‘War of the Roses’ [yes I know nitpickers, it wasn’t called that at the time]).
One of Owen and Queen Dowager Catherine’s sons was Edmund Tudor, a particular favorite of his half-brother the king who made him Earl of Richmond and arranged his marriage to the 12 year old heiress Margaret Beaufort. She was the king’s cousin (but not his half brother’s), a granddaughter of John Beaufort, the illegitimate (but later legitimized) son of John of Gaunt and Kathryn Swinford. The fact that Margaret Beaufort was already betrothed at the time of this wedding would later prove an issue.
A reminder: a betrothal is less than a marriage but it’s much* more* than an engagement. It’s a legally binding contract for marriage that prevents either party from legally marrying anybody else. It’s acceptable to refer to the couple as husband and wife during a betrothal, it’s even fine and dandy [so long as both parties are of a reasonable age and their parents are consenting] for a betrothed couple to go ahead and have sex, and any children conceived or even born during the betrothal are considered legitimate. It was similar to a city hall wedding today- a legal marriage but one that’s not been blessed by a religious figure, though of course this being the late middle ages century that religious blessing was more than a formality- the betrothal was the “render unto Caesar” and the wedding was the “unto God what is God’s” part.
Now the phrase “who God hath joined together let no man put asunder” is today pretty words, but as Henry VIII would one day find out it meant that a king could not declare a marriage invalid once it had been blessed by the church. However, since the betrothal was a legal contract, not a holy one, there was some argument that the king could legally break it. There’s hair splitting either way- the fact that the betrothal was agreed to by her father when Margaret was a baby and not Margaret herself and thus she did not break a vow came into play- much later on, not at the time- but the point is that in the case of his cousin Margaret Beaufort Henry did break the betrothal and marry her to his half-brother Edmund. She was literally a child bride [at least by our standards] and though her betrothal had not been consummated her marriage certainly was because within a year she was a seven months pregnant widow of 13 when her husband died as P.O.W. following one of Henry VI’s battles against the Yorks.
So many novels and movies and TV shows of wildly varied quality appear about Henry VIII long after all six wives have been done to death that it’s surprising nobody’s really taken on Margaret. She’s also the character who would be easiest to portray- fictionally at least- as a manipulator/schemer/warhorse akin to Livia from I CLAUDIUS. Twice betrothed at 12, she and her baby Henry both almost dies in childbirth when she’s 13 (it probably left her unable to have another child- leastwise she didn’t). The nation is completely in civil war before her wounds have healed and her half-brother-in-law/cousin is the insane king who’s losing to the pretender some years and then back on top some years, and she has a relationship with her sister-in-law Queen Margaret who’s the real power since Henry VI is so often insane and Q Margaret is out to protect their son, so basically it’s a front row seat to the War of the Roses.
Margaret Beaufort Tudor learns to dance fancy moves to avoid imprisonment for disloyalty to either faction, she enters into familial alliances, marriages of convenience, exile, learns how to give a holy oath with a smile on her face when she has every intention of breaking it, etc., all to protect her own life and that of her baby. From what little is certain about her in the record you can tell she was no shrinking violet herself and it had long occurred to her “why not my baby for king?”
Eventually her son grows up, becomes- somewhat illogically- the Lancastrian claimant to the throne, and after killing Richard III on Bosworth field (and possibly the princes in the tower [who were illegitimate because of a betrothal, or were they? or were they killed by Richard III? or by Margaret Beaufort’s scheming? or by plague?- lots of fertile uncertainties for a novel) her son Henry, possibly a bastard himself (due to the betrothal matter), a bastard member of the House of Valois through Queen Catherine’s morganatic union with a Welshman, a descendant of a bastard son of a fourth son of Edward III and a nephew of uncertain legitimacy of an insane half-uncle who was king, becomes King Henry VII with the most filament thin links to legitimacy of any English king since William the Bastard.
And so the possibly illegitimate Henry who’s the descendant of many bastards and questionable associations marries the possibly illegitimate Elizabeth of York, sister of the possibly illegitimate princes who he or their uncle Richard or somebody else possibly murdered in the tower, all the children and grandchildren of men who the Lancastrians have spent many years and killed and lost thousands of men in proving had no rights to the throne, and he does this so he can have a legitimate and unquestioned claim to the throne. And it works- there’s some fun with pretenders that lead to rebellions but by the end of his reign this “bastard Plantaganet, bastard Valois, and bastard Tudor” as he was called in his own time, is the first king in living memory to not have to worry about his throne. And his mother remains forever a presence in his life, including in the choosing of a bride for her grandson Arthur and, upon Arthur’s death, the new heir little future Henry 8. Would make a good novel.
