I can't find the title of a manga that I started reading some time ago

It's in a medieval ambience with the main character, a boy crossdressing to take his sister place who was called to a castle to get married.

Thank you in advance for the help

Maybe this one?!?
Kiss Me Princess

"The world is a dangerous place to live, not because of the people who are evil, but because of the people who don't do anything about it." - Albert Einstein

Kiss Me Princess?

Be kind or get banned

Thank you but it's not that. It was a japanese manga ^^

Shounen Oujo maybe ?

Quote from Thaa

Shounen Oujo maybe ?

Couldn't be. His sister was the princess there, she wasn't getting married to anyone.

I can think of two others besides Kiss Me Princess, but they're both manhwa (do Koreans have a special liking for that kind of thing?) I'll mention them just in case: A Night of a Thousand Dreams and I-Ren.

I can't remember a single manga with that theme, off the top of my head. Was it BL or no?

It was shounen ai

If it's shounen-ai, this thread should probably going go in the Yaoi/Yuri forum.

Anyway, definitely not sure about this, but is it 5-nin no Ou?