Pellinore X Guinevere's Sister?!
(Source: Le Morte D'Arthur, by Thomas Malory)
Okay. So... this was a something that was brought to my attention by @wandrenowle
There's this very small detail in Le Morte D'Arthur that is so obscure that, as far as I see online, most Malory enjoyers never discuss because it's so obscure. But despite that, it's still pretty shocking to any well-learned Arthuriana enthusiast like myself: Merlin prophesizes to Arthur that he will wed his sister to King Pellinore.
As seen in the second image above, it would seem that Aglovale, Percival, and Lamorak are referred to as Nephews of Arthur, implying that, yes, Pellinore has legally wedded one of Arthur's sisters.
The headscratcher obviously comes in the form of "Who?/which sister?". There are only three stated (half-)sisters of Arthur in Le Morte - Morgause, Elaine and Morgan - all of whom are already taken by Kings Lot, Nentres and Urien, respectively.
So, who on earth did Pellinore marry?
One might be tempted to believe it's Morgause, since her husband dies early in Le Morte and thus free to remarry. Or that Malory has (unintentionally?) introduced a fourth sister of Arthur for Pellinore to marry.
The problem with either possibility is that Sir Lamorak, Pellinore's son, is presented as Morgause' lover and a possible suitor, which would be massively problematic under Medieval culture since that would be incest and illegal under Church Law.
It should be noted that Arthur supports a marriage between Lamorak and Morgause, which, again, would be extremely wrong and ridiculous if they were related by blood:
Rationally, we have to strictly discount Morgause as Pellinore's potential wife. Likewise, Morgan, Elaine and any unmentioned sister are also off limits because of Lamorak's narrative. So, what now?
Kenneth Hodges, in the book Mapping Malory, proposes a very interesting solution: the "sister" of King Arthur being referred to here is not a blood sister but a sister-in-law. In Medieval language, "sister" could mean either your own female sibling or a female sibling from your legal spouse. Similarly, nephews could refer to one's blood nephews or nephews by marriage - Guinevere does refer to Sir Gawain as her nephew in other texts.
Hodges believes Pellinore's wife could be Queen Guinevere's sister:
(Source: Mapping Malory, by Dorsey Armstrong and Kenneth Hodges)
So, we have a possibility that Pellinore married one of Leodegrance's daughters and is (in Maloryverse) the mother of his legal sons, including Percival and Lamorak. This neatly solves the problem of Lamorak wooing Morgause, as "affinity does not beget affinity" if they're only related through Guinevere.
This concept is further bolstered by certain details such the claim by Percival that they have Royal Blood on both sides of the family, which discounts the half-sisters of Arthur as they are the daughters of Duke Gorlois and strictly not Royal lineage (Although, Hodges admits that can be disputed):
If the notion of Pellinore marrying a sister of Guinevere's is taken as fact, this puts an interesting dimension to the feuding in Malory's story. Because it means Guinevere's brother-in-law and nephews are sworn enemies of Arthur's other relatives, the Orkney family:
...Making one of the central conflicts in Le Morte D'Arthur not just a blood feud between the families of King Lot and King Pellinore, it's also a blood feud between the families of Arthur and Guinevere
(Special Thanks and Credits to @wandrenowle for bring this topic to my attention and providing the reference material. Always cool and much appreciation)