It's related in a sense that it is the FL who has an ability. For Im Sol, it's to go back in time, for Nam Hong Joo, it was to see the future in her dreams. In both dramas, fate is involved. Both also have very complex stories.

Cinematography is similar, and it's similar in a sense that both of the main characters are in a similar situation, and they find love :))

Same young female lead, she plays as twins in both dramas, except in the King's Affection, she plays a twin pair of a girl and a boy. Something happens to one of the twins in both dramas.
Again, Joseon Era setting, and political plots.
There is also a parallel of the main leads meeting at a young age, and starting to have feelings for each other since then.

First parallel is the setting, both are set in the Joseon era. Next is the very political plot, with many plot twists and love rivalry. Yet, the main leads try to find how they could be able to love each other despite their obstacles.


WARNING: Next paragraph may contain spoiler

Another parallel though is that the main girl enters the palace as the male lead's concubine.