Jang Young Shil (2016)

Both are happening in the same time frame. In both Kim Sang Kyung and Kim Yeong Cheol are playing the same characters, Kim Sang Kyung plays king Sejong and Kim Yeong Cheol - king Taejong. In The Great King Sejong Jang Yeong Sil is an important supporting character, while in Jang Yeong Sil he is the main character.

In splash splash love we get a taste of science and innovation, if you want more of a story showing these things you should watch Jang young shill it focuses on king Sejong's interest in astronomy and the real Jang shill a inventor

Both are about sons of noble from a lowborn mother who will rise above barriers of social class, nepotism, scheming etc to do exceptional things in their field at their time and place. Political drama, jealousy, friendships,and underdog are major themes, YoungShil deals with astronomy and science while HurJun deals with medicine

Both dramas staring Song Il Gook. Both rags to riches kind of story. Both characters has a loyal side kick from since childhood. Both have forbidden love with a princess.