
Thank you for the spoilers . Lancelot is the best and deserves to be happy :) I haven't read the korean raws but the spanish scans.
To add on to the spoilers
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Original Charlotte who died during the battle with the duke was tempted by a demon summoned by her hatred. The demon forms a contract with her to give her another life not as Charlotte but as the beautiful older sister of the Prince. She wants to be someone else because the shitty red hair Duke tells her," I won't love you as long as you are Charlotte." so with her twisted love she abandons everyone who she treats as pawns anyway and lives on as the princess. BTW she never cared about Lancelot and wanted him to waste away after her death grade A bitch.
When our MC comes along Original Charlotte is pissed off seeing her old body walking around since the demon told her during the contract that her old body would just die and disappear.
Lancelot finds out early on that this is not his Charlotte he goes into the Magic Tower(he is the boss of the Magic Tower btw ;) ) reads more into soul magic. He cast a spell on our MC revealing her true self(korean self). Lancelot is angered and is about to do something to the MC but she ends up kinda waking up from her rest thinking it's a dream and kisses Lancelot.
This flashback>>>>>is shown in later chapters but after that interaction^ he cast a spell to locate Original Charlotte's soul. He tracks her down to the castle and right there he is stopped by the Demon who tells him everything that occurred.
Poor baby :( Lancelot feels devastated because his old magic tower master abandoned him and now both the ladies of the house have also abandoned him. He starts feeling very lonely casting a spell that i think would've killed him but the MC interrupts him on time :). She scolds him for missing 1 or 2 days and tells him not to disappear. From then on Lancelot grows to love our MC who he sees shows love in her eyes when she looks at him. Lancelot wants HER to tell him the truth of who she is so he can start calling her by her true name but the both have misunderstandings @_@. He also says things like, "I just want to be loved." :C
There's a grand banquet later on and Original Charlotte now Princess hints to Lancelot who she really is by bringing up a childhood memory ;) but he don't give a fuck anymore and just ignores her ass/plays like he doesn't know the secret. During this our MC is worried that Lancelot will find out the truth about his Original Charlotte(hahah too late he been known^) since OG Charlotte already confronted the MC about the soul switch. MC lied to Charlotte saying she is her maid instead of the truth which is good imo lol cuz OG Charlotte is crazy. There's so much to cover @_@ so anyway Lancelot proposes an engagement to our MC that's why they go visit the Castle. Lancelot is the Tower Master and can save the land from a terrible Drought that is going on in the kingdom. He can bring fame and prestige to Charlotte's house instead of allies of the duke and the duke himself bringing it down to ruin.
After Lancelot cast a spell for rain all of the nobles are shocked
(⊙…⊙ )because their kingdom is ignorant of magic and thinks it does nothing lol. OG Charlotte is also surprised by Lancelot's magic since he only showed her a tiny glimmer of what it can really do. Our MC ask Charlotte, "Do you find him useful now?" she responds "He's an annoying pest now" >:(. OG Charlotte is engaged to the red hair donkey Duke so she got what she wanted but our MC still ask her, "Do you regret it?" and she says "No, i'm happy now." but she seems unsure.
The kiss is hot as hell :O it was basically during the banquet they both go outside. listen to the music playing, start to dance when the MC says, "i love you Lancelot" and KISSES the hell outta his cutie face. He ask while blushing, "Please don't tell me this is a joke or i will punish you" Then she kisses him again and he kisses back :). Towards the latest chapter i read it seems that OG Charlotte might be planning to kill our MC :( also the annoying red hair Duke is bothering our cute couple pffft getaway.
Also the next day after the kiss, our MC ask Lancelot if their kiss last night was bad or something since he is acting like normal. Her question shook him xD he grabs her hand and puts it on his chest and says his heart is beating too much around her but since he is still her butler he needs to be professional xD. They end up kissing again ;). Such a cute couple!

I read it here but its in spanish xD
https://lectortmo.com/library/manhwa/51772/el-mayordomo-de-la-dama
korean:
https://newtoki69.com/bbs//board.php?bo_table=webtoon&wr_id=3204541

Here’s a site I tend to go to for some raws:
https://newtoki69.com/webtoon/3204541/그-아가씨의-집사님?toon=일반웹툰
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Lancelot actually does figure out that Charolette isn't the original pretty early. I forgot which chapter, but I believe it should be in the upcoming chapters. Of course, he attempts to get rid of the MC without the MC really knowing it, but because of her warm interactions with him, he doesn't find the courage to do so. Instead, I believe he slowly starts to accept this new Charolette.
Now, after this is all said and done, the two go to the palace where they meet the prince and the princess. For those two, I don't know if they're siblings or engaged since I can't read Korean.
But guess what?
We got ourselves another two face. Yes, the princess acts all so cute and elegant, but in reality, she a captial B to our Mc.
And you know what's even more bs?
It's my theory, but I have read somewhere that has confirm it that the princess is the original Charolette. Yes, that's right, the original Charolette who's has such a trashy personality behind that elegant facade.
How?
From what I've seen, the original Charolette seems to have made a deal with a different wizard who isn't Lancelot to live in the body of the princess as we get to see it being told by that exact wizard to Lancelot.
Feeling betrayed by the woman he loved, Lancelot would have lost his sanity if it weren't for our MC coming in to talk to him. After that talk, I believe Lance starts to fall for the MC or at least become affectionate to her.
When the princess finds out, I guess she becomes envious (Like why b$%^#?! You left our boy for another, don't come running back!) as she watches the two become closer and closer.
But to end this in a good note for now, our MC and Lance kiss!! ε=ε=(ノ≧∇≦)ノ
Yes, ladies and gents, they kiss and seem to have become a couple or at least affectionate with each other!