i dont know.. but for some reason i always like a prince or duke or count or sheikh or something like that having a romance..

i mean who doesnt love a prince on the white horse? ^^

if you know any stories with royalty in it^^

Some categories that might be of interest to you:

King
Prince/s
Royalty
Noble
Fallen Nobility
Sheikh

You can search by genre and narrow it down further with category tags, so you can specify, for example, Yaoi with prince/s. Fiddle around with that a little - it should spit a good number of manga out at you.

Royal Fiancé by Kamon Saeko and Asuma Risai,
Taiyou no Kikoushi by Maruya Kae,
Hashire! Oujisama and Juusha to Oresama by Yamakami Riyu,
Ousama Game and Oujisama Game and Kaizoku Game by Takagi Ryo,
Kyokutou no Hanamuko by Maeda Momiji,
Chapter 7 from Senaka kara Daite by Takenaka Sei..
I'd say Kyou kara Ma no Tsuku Jiyuugyou! by Matsumoto Temari and Takabayashi Tomo..

Sekai wa minikuidesu..shika shi! Yūjō, yūki, tsuyo-sa wa ikinokoranakereba narimasen..Tiruendo!