Iljimae

I know the dramas are kinda random, but if you came to see Iljimae to see Kim Yoo Jung in her child actress days, then I definitely recommend you at least see her scenes in Grudge the Revolt of Gumiho. It's her first lead role in TV. If you see her romancing Yeo Jin Goo (her lover in Moon Embracing the Sun) in Iljimae, definitely check out Gumiho Fox Child for her romance with Lee Tae Ri (formely known as Lee Min Ho born 1993, he's another lover of Kim Yoo Jung in Moon Embracing the Sun).
In both dramas though, Kim Yoo Jung plays a good kind hearted girl. There are also a few scenes in both dramas that are quite similar. In Iljimae, Kim Yoo Jung enjoys the company of a bird while in Gumiho Fox Child Kim Yoo Jung enjoys following mostly fireflies and sometimes butterflies. Another scene is where Kim Yoo Jung is helping one of the young male characters heal their wounds. And another one is where Kim Yoo Jung's adult version Han Hyo Joo is enjoying the lanterns while being watched by one of her love interests in Iljimae is similar to Kim Yoo Jung in Gumiho Fox Child where she was also watching the lanterns while her male love interest looks at her so lovingly.

Both dramas have both the main male leads as brothers but both characters don't know that they are brothers. Both the father and mentor of the main character for both dramas was played by the same actors. Finally, both dramas are about avenging the death of a father, but also becoming the true king that the people of Joseon deserve.

A remake of this drama. Both Lee Jun Ki and Jung Il Woo portrayed their roles perfectly and they both are very hot <3

Both share a FL running an inn/boarding house, a ML who lost his father which causes him to hide his identity, & a family secret.

Both of those dramas are similar, deciphering into the Joseon Era and explaining the male lead as they have the same rags to riches journey with rising to power and how they became to be.