I think it's a movie for only science and math and fantasy lovers but Lee Min Ho and Kim Go Eun are excellent in The King: Eternal Monarch. And I truly didn't like the evil uncle. His acting must have been superb for me to dislike him so much. I know the King took her as his wife in talk only and I would have loved to see him take her as his Queen in the parallel world.
However, the movie lets us see toward the ending as their hands age mysteriously that we assume they are young forever because of traveling between the two worlds.
I have enjoyed seeing Lee Min Ho act in The Inheritors (The Heirs) and Kim Go Eun act in Cheese in the Trap and have enjoyed both of them immensely. Personally I would love to see sequels to both movies but realize the stars have also aged. But I can't wait to see other movies starring both of them.