What happen to the mc's original body?? did it not exist in that timeline??

If you want to know spoilers please read down
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Well lets just say that the mcs original body doesnt exist im this timeline but if i remember correctly his friend(?) brother(?) i forgot their relationship, remembers him. So when he learned that the “enemy prince” changed in this timeline, he was happy and knew that is him. They will end up meeting and having a great reconciliation (idk the right word)

Do the brother go back in time as well??

Yes he basically remembers that he went back but i actually dont rember if its just him that remembers (with the mc) or the whole clan(?) but yesh

oh if the whole clan regressed as well that explain why there are other member on the somekind of festival and they are finding the mc??

perhaps perhaps! Or that the brother tells to get spies to check on the mc!