Some times I wonder if people ask these sorts of questions as a contest. Always up for a challenge and it is not like we are giving legal advice or doing something that will break someone if hosed up this time so I will start.
Surprisingly little history online about such things compared to some other places I have seen (I have a local history book of the tiny little village I am in that has far far far more detail than things I have been able to find here). I would half expect high res photos of everything they can get online, transcriptions and descriptions with this being Grade I listed but I guess not. Did get a wonderful story about them being preserved during world war 2 though.
Anyway what I thought might help would be that inscription. Found a higher res image (
https://www.istockphoto.com/ca/photo/stained-glass-in-kings-college-chapel-gm147023101-8975360 ) and "vraye fidélité cherch le profit" (give or take accents) returns nothing here and I don't want to guess at the bottom line (my knowledge of old school upper class/religious French (
https://www.theclassroom.com/first-english-king-speak-english-22560.html ) is not quite up to the task of guessing at the blanks/blurry bits, though I would wonder if the second line is some kind of negation of that as modern French would have it as something dealing with seeking profit which is odd for old religious stuff (or at least profit motives are generally expected to be a bit further along in history)).
Someone named Hilary Wayment (obit:
https://www.independent.co.uk/news/obituaries/hilary-wayment-489983.html ) apparently did a fairly in depth study on the glass there and a few other places (Corpus Vitrearum Medii Aevi: Windows of King's College Chapel, abebooks link for the author
https://www.abebooks.co.uk/servlet/SearchResults?an=hilary wayment&cm_sp=det-_-bdp-_-author . 0-19-725918-9 being one number for one of them) but the books are out of print, seemingly not available online and I am not invested enough to drop the serious coin they seem to command.
That said I should note that in all this it might just be the artist's mate he stuck in there for giggles -- if this is a nice lesser part of the whole work then such jokes are common.
