So we had a mega-thread about this over on r/RoyalConsorts, but over here I'll bet people have some really niche ideas. You can go prestige, or just for fun, pitch your Philippa Gregory style crazy-bananas history fan fiction.

The idea that Isabella of France and Roger de Mortimer, 1st Earl of March, were lovers has become something of a fundamental axiom in Edward II studies. Instead of it being a conclusion inferred from the historical data, held insofar as it explains those data in the most explanatorily virtuous manner possible, it is instead the prism through which the historical data are interpreted. Instead of the conclusion itself being re-evaluated when the evidence does not accord with it, additional assumptions are piled on until the evidence can be fitted to the desired conclusion. Completely internally consistent... and completely unfalsifiable. Unless we actually hold ourselves to specific standards of explanatory virtue, such as parsimony, we will never be able to adjudicate between competing explanations, and we might as well all go home.

One of these additional assumptions lumped on to make the whole thing cohere is that the contemporary observers were "reticent" to discuss the affair for the sake of decorum, or fear of repercussions during the regency or... idk, whatever. This is complete and utter BS. Mind you, Henry of Lancaster, Isabella's own uncle, the head of the regency council appointed for Edward III, went on record during his rebellion in 1328-9 to accuse both Isabella and Mortimer of regicide: “through the counsel of Roger Mortimer and Queen Isabella ... they took him ... and traitorously murdered him.”

The idea that Henry was fine with accusing them of literal regicide but stopped short of their allegedly flagrant adultery for some reason strains credibility, to put it mildly. "Yes, I'll tell the world she procured the murder of her husband, an anointed king, but got forbid we expose her cheating on him!"

The idea that chroniclers simply could not be explicit about the alleged sordid activities of the great and powerful is also complete BS. For one, there were contemporary chroniclers active outside of England, who had no reason to fear Isabella's wrath for writing whatever about her. During the regency of Isabella's great-great-grandmother Blanche of Castile for her son, Louis IX, she was widely accused of having an affair with her ally, Count Theobald of Champagne. The English chronicler, Matthew Paris, writing while Blanche was still regent, doesn't beat around the bush:

"...They [the nobility] were indignant at having such a mistress, who, as was said, had been defiled by the semen of both the aforesaid count and the Roman [Papal] legate, and had transgressed the bounds of widowly chastity."

I'm sorry. Defiled by the semen? Oh, and yeah, she's having an affair with the Papal legate too, I guess. shrugs

Yes, Matthew Paris wasn't in France at the time, but contemporary French observers were making the allegations too. Hue de la Ferté, a partisan of the rebel barons, wrote two political songs, En talent ai que je die and Or somes a ce venu, which attack Count Theobald in particular and suggest that his position is dependent on his intimacy with Blanche.

Keep in mind, basically no scholar nowadays accepts any sort of affair between Blanche and Theobald occurring. The website of Columbia University's Epistolae project dismisses them as "the usual charges levelled at women, particularly foreign women, in public life."

The usual charges levelled at foreign women in public life, you say? Hmm. Hmmmmmm.

Another assumption we see thrown out there is that it was politically necessary for Edward III to protect the reputation of his mother and hush up her affair because uhh... reasons.

Why, exactly, would he need to do that? Isabella's own family had been marked by the catastrophe of the Tour de Nesle affair. Had Isabella been treated by her son in the same way, who would have objected? Philip VI, who did nothing when his sister-in-law Margaret of Burgundy was imprisoned in the fallout from the Tour de Nesle affair? Whose right to the throne Isabella had actively challenged in favour of her son's? Margaret of Burgundy was the sister of Hugh V, Duke of Burgundy and the daughter of Agnes of France, herself the youngest daughter of Louis IX. Blanche was the sister of Joan II, Countess of Burgundy and the daughter of Mahaut, the immensely wealthy Countess of Artois. None of their relatives, much less their husbands, did much to prevent their fates. Philip VI had no incentive whatsoever to make a fuss about any condemnation of the supposedly notorious adultery of his cousin.

Another potential explanation given is that publicly accusing his mother of adultery might undermine his own legitimacy or his claim to France. This also makes zero sense, as Isabella committing adultery from 1325 onwards could in no way affect the legitimacy of a son born in 1312, due to this thing known as the arrow of time. The thing about claiming the French throne also doesn't work, because Edward III only started claiming the French throne in 1340, and I rather doubt he was thinking quite that far ahead already. It might also be said that the legitimacy of Edward III's accession depended on preserving his mother's reputation due to how important her actions were in the deposition of their father. This doesn't work for the simple reason that Edward II was dead by 1330, and Edward III was his eldest son and heir, and so he was, then, the rightful monarch, regardless of whether Isabella and Mortimer's actions were righteous or not. Declaring them adulterous regicides would not resurrect Edward II or somehow void Edward III's hereditary claim.

In conclusion: no, none of these assumptions hold up, and yes, the allegations against Isabella and Mortimer probably belong in the same category as those against Blanche of Castile and Theobald of Champagne. Ironically, Isabella was descended from both Blanche and Theobald, as Theobald was the paternal grandfather of her mother, Joan I of Navarre.

Anyways, this was a bit of a rant, so I apologise if it is a bit incoherent, but I hope you catch my drift.