Yep im pretty sure it is also mentioned pretty early on, cause aseph originally fell for the sister, but she was fated to the prince so aseph wasn’t happy or sum.
Big spoiler...
Asef didn't even love the twin sister in the priginal life. The original twin sacrificed her life to save asef when he was young and therefore asef lost his fated partner from a young age. He developed feelings for the twins not out of his own will he only feel a connection to the twon sister because she was the closest thing to his own partner.
Oh shit. Thanks lol spoilers are actually one of my favourite things cause they give me a sense of what is going to happen
I saw some spoilers on facebook that the second twin sister (forgot her name) had the same mark as the prince so yeah its still the same