Swapped with the Villainous Fiancee

"Eve Ambrose! I am breaking my engagement with you and I shall be marrying Diana Asteria! " Darian Alinac, the first prince of Edrutia Empire said to his political marriage partner.
Not only was he cheating on his fiance, but he also pointed out the misdeeds Eve committed against Diana.
"Fine...I understand His majesty's wish." the dismayed Eve said as she went out of the banquet hall.

However the next day Darian wakes up in the body of his ex-fiance.
"Do you really think that this political marriage can be broken? Listen dumbass you will be stuck in this body until marriage between 'Eve Ambrose' and 'Darian Alinac' will be finalized for the sake of Astaseul Empire .' His ex-fiance said as she visited him in his own body.

Why was Eve so bent on this political marriage? And was she really Eve Ambrose?