I recommend "Qing Chuan Zhi Xue Shen Crown Princess". The male protagonist of this book is the little prince Yinreng. Although he is not the 13th Prince you mentioned, the story is very interesting. The protagonist becomes the crown princess by signing the most advanced soul marriage contract in the universe. The interaction and funny scenes between the protagonist and the little prince are very exciting. I hope you like my recommendation. Muah ~