Two more below the cut, as well as explanations, details and some references!
First PSA: naturally, hairstyles were fluid as they always are, the horns came up before the 90's (but really became widespread by then), some people kept more old-fashioned hairstyles longer, and of course, Monchevy themselves didn't stick to ONE hairstyle per decade, but that goes without saying.
My point was to kind of explore the transformations over the decades, and the predominent, more popular/fashionable styles of a decade with them, as I thought it could be fun. It is fairly difficult to get a good grasp of how it evolved back then, even more difficult for some paintings to find the exact date and trace a decent timeline, and therefore I wanted a sort of simplified but easy to understand visual for it (not to mention, I enjoy simplification for character design purposes, so it was a good exercise).
Now onto some additional notes and visuals:
Here we have Philippe (x2) and Louis in their teens, displaying the wavy bangs with the very curly hair beneath. Unfortunately, we have no confirmed depiction of chev in his teens. It is rather easy to find references of many other young men and boys with this hairstyle (and ofc, many variations of it), but since it's pretty hard to find properly dated paintings, I stuck to what I know. As for the note regarding Chev having straight hair, it just so happens that a couple of written accounts state that he deliberately made his hair wavy/messy (in the next decade). I'm not citing them here because I'm haven't been able to confirm all of the sources yet.
Back to Philippe (x2) and Louis as again, they are reliable sources and I can date them pretty easily. Contrary to popular belief, most young men didn't wear wigs at the time. Philippe likely didn't start wearing wigs until his early/mid 30s. The infos are less precise about Louis, as we know he lost quite a bit of hair due to his typhoid fever in 1658, and wore wigs at least for a while to cover that---however, some sources say they regrew afterwards and that he only fully switched to wigs in his mid 30s as well. As for Chev, once again, no confirmed painting or depiction. We do know that most young men, as stated, wore their natural hair and that négligé hairstyles were popular; in a citation that I still haven't fully confirmed the source of, Philippe himself describes his hair as "slightly wavy and deliberately messy by fantasy", which is my main inspiration.
We most likely transition to wigs for Philippe in this decade. I wanted to have some fun with Chev's hairstyle and gave him a military one, which could either be styled with natural hair or wigs--I went for natural hair in his case. References are Philippe, some guy, and a drawing from a book about hairstyles and hat.
We are slowly transitioning here towards the horrors that became really popular in the 90's. The bangs are going away, and the top of the head is widening. The first portrait I chose for reference is Chev, despite this being a post-mortem one and therefore not specifically dated. However, he looks to be in his mid-forties, and the hairstyle matches that which was pretty popular in the 80's, so it feels like a correct reference. Here we have Chev, Philippe, and le grand dauphin.
And finally, we reach the horned up 90's. Here, Philippe, le grand dauphin again, and Chev, illustrating this wonderful era.
I chose to add ribbons in Philippe's hair, as he was described (albeit ambiguously) by Saint-Simon, as adding many ribbons to his... wigs? The thing is, in the original sentence, it is hard to tell whether he actually means the wigs, or in general. However, it seems like all historians interpret it as meaning the wigs, and it is funny, so why not.
Also, I want to add that a lot of references are engravings, as these tend to be much easier to find the dates of, lol.
