Why would the scion or more likely the father of said scion of the Royal House of Kent marry the only legitimate child of a deceased sonless king of the Frankish realm?
Aside suggesting you compare and contrast the size of the kingdom of Kent and the Kingdom of Paris, I want you to focus on the particulars of the rules of succession in the Frankish Realm.
Salian Law. Only sons begat by sons can inherit the crown. Does it mean they leave their daughters penniless and adrift? No.
Though her own father and probably brother had been killed by her uncle Gondebaud, Chlothildis, Bertha’s great grandmother (a princess fiercely Roman Catholic) was bespoken by Chlodoweg (that is her great grandfather). And her dowry was consequent.
If Bertha was just a royal princess, she still inherited quite a few choicest pieces of her father personal treasure. Her half-sister, another Chlothildis called the Superb orphaned like her was put into the care of Radegunda their step-grandmother. Later on, her decision to forcefully leave the convent was to fill quite a few anxious pages from Gregory of Tours’ diary. Eventually successful, she knows she would live free and enjoy a peaceful non-recluse life. A life clearly comfortable!
So let’s nor delude ourselves. Bertha was not going to hand out the Kingdom of Paris to a Saxon prince. She was not going to marry him empty-handed either! Only legitimate daughter, one can imagine a very substantial dowry and inheritance.
Gregory says she was handed to the ‘man from Kent’ by her parents. Since Charibert was dead, who were said parents? Most probably her guardians.
We are clueless as when Charibert married Ingoberga, just like we are clueless about Gunthramm own matrimonies. We know that in 566, their brother Sighebert marries the Visigoth and Arian princess Brunhildis and soon after their younger half-brother Chilperic follows suit with Galswinthe, Brunhildis sister.
Gregory makes great fuss of the royal lineage of the two sisters. He implies Charibert’s consort was not of a similar rank. Royal, Ingoberga was not. It does not say she was of an ancillary background. Far from it. She gives a dressing down to her husband when Charibert takes wives/concubines of a lesser rank by showing him their plebeian father at work. Not royal true; but certainly aristocratic.
Some grants suggest Ingoberga of Tours was related to bishops and of a senatorial rank family. Frankia had no Senators. Yet Gallo-Roman families who had belonged to aristocratic Gaul families and in her case families high enough to count Senators in their midst would naturally be proud of their glorious past. Maybe not royal, but her last and very dignified days are given a proper bow by Gregory. Bertha was not royal on the maternal line: she could only be ashamed of the repudiation of said mother (and possibly a nasty temper).
Ingoberga had given no son; Ingoberga had remonstrated her husband. Charibert was no Henry VIII Tudor; his ex-wife carried on living in Tours. As Tours was a former capital of the realm, one can imagine Ingoberga living in the old palace educating her daughter … or not. Charibert was son less and his heirs were short lived daughters but for little Aldeberga (her real name) and baby Chlothildis. He had a son finally dead soon enough then poor Charibert died.
Chlothildis mother was either repudiated already or dead. Bertha was older and legitimate. Who were their guardians? Judging from Chlothildis, the two girls must not have been 10 years apart. An age where little girls can be spoken for but not nubile to enter physically into matrimony.
On one side, Chilperic and his wife Fredegunda. The half uncle suspected of killing his other wife Galswintha and allowing the murder of his own children including the rape of his daughter Basina and Fredegunda totally suspected of having ordered the murder of her brother-in-law Sighebert (and with this woman, one may need to review how Charibert died: poisons already existed, right?). Shall we add Gregory nicknames Chilperic Nero?
In 567, all this blood-shed had not yet been spilled but the atrocious behaviour of Chilperic toward Athanagild’s daughter must have already got tongues wagging. If Brunehildis and Sighebert were providing the impeccable lineage of what was accepted for aunt and uncle, Chilperic and his whore Fredegunda were not.
Gunthramm, king of Orleans was possibly known for an erratic love-life; still he was also known for being generous with the church and much later would become Saint Gontran at the request of his subjects. Gunthram (Battle Raven) was not perfect but seems to have been a decent uncle.
In this equation, one must keep in mind Ingoberga the widow whose good deeds pleased the Church and naturally Radegunda, the very virtuous step-grandmother.
Bertha would be raised under the watchful eyes of her mother and grandmother and her uncles King of Metz and King of Orleans would have first rank as guardians. Chilperic could keep Fredegunda, get bits of his deceased brother kingdom but his opinion on the matter of his niece future was less powerful.
Years passed. Sighebert is assassinated and his son little Childebert is himself raised by the now dowager Queen Brunehildis. Brunhildis hates the diabolical couple but her virtue is far from perfect. Would Radegunda relinquish her watch? No.
Our two ladies, the one who repudiated the King and the one who was repudiated keep their daughter and grandchildren safe. Far from Paris, Soissons and close enough to the Orleans kingdom to find asylum in case of danger.
In 575 Sighebert is assassinated; in 577 Gunthramm sons die. All of them. Gunthramm decides to name as his heir his Austrasian nephew. Not Chilperic’s sons. There is no love lost between the half-brothers, nor between their wives.
Would Radegunda allow her step orphaned grand-daughters to set foot in this hornet nest? No.
Bertha along her sister is educated fast from the three courts. Gunthramm must have made sure his nieces would not be found lacking. At mote distance, Brunehildis would have played the girls from the late king of Paris (a womanizer, true but a peace lover if we believe Venantius Fortunatus and he would know as Radegunda own bishop). Brunehildis will play a part in Kent conversion to Christianity unlike Fredegunda.
So we have it. Bertha may be brother and father less; but she is not missing in the department of kind guardians. Though she is clearly not missing in her share of the wicked uncle and the evil aunt.
And this is but the tip of the iceberg. Bertha is Charibert only legitimate heir; as much is true.
Now let’s have a look at her uncles’ sons. In 577, Gunthramm renounces to having son and starts flirting with the notion of allowing his nephew via Sighebert to be his heir. Said putative heir is only 10. Chlothildis is possibly 11-12. Bertha is now… 15? But a catastrophe occurs. Chilperic’ sons die one after the other. He was careless with his heirs via Audovera; God punishes him via the children Fredegunda has given him.
In 584 AD when Chilperic dies, he leaves a four month old baby boy whose parentage is debatable. And this is it. If in 584, baby Chlothar is not nor given to Chilperic as a child, the crown goes and the entire realm to young Childebert who is 17. And this is it. Because Childebert is the last male heir.
… And we have Bertha.
True Salian law applies. But you see now how close to a dynastic crisis the Merovingian bloodline has been sailing and how important is insignificant Bertha.
Do not forget that if Chlothar II is indeed a bastard, it only means one thing. In 606, when Chlothar gets rid of his Austrasian family, the only true heirs of Chlodoweg are to be found in Canterbury.
For Kent and the Oiscing royal family, marrying a Mrovingian princess orphaned yet heress to estates probably wider than their own realm was a diplomatic coup. … Do not forget we have not even started yet to discuss a trade treaty!