The unknown pendragon (fgo x pendragon reader)

We all know the bastard "son" of king arthur, the knight of rebellion. He who proclaims that he is the only heir to the throne, but what if i tell you that "he" is not the only one. This is the story of the prince that is unknown to his family but known to many. y/n pendragon, the son of guinevere and arthur but when...