Do you remember what colour his hair was?
Shoulder length black hair when in the modern world, black haired 8-10 year-old prince in joseon.
Sorry, the ones like reborn as the enemy prince and a modern man who got transmigrated into the murim world came to mind.... But they don't exactly match ur description:(
Ay, lemme get that link tho
No prob! I appreciate you noticing this question and trying to help!
I read it before but i forgot to bookmark it. Tis about a modern world inventor who's reincarnated in Joseon but in the body of a child prince and there he started to apply his modern knowledge to improve the kingdom and prevent the chaos in his family. Anyone?