I'll make a bold prediction, Grandpa knows everything, from the fake marriage to Ji than and Ah Jeong's relationship,…
omgg I also had this theory that grandpa knows everything because it was really fishy when he accepted Ah Jeong and i think he sensed something during the scene where Ah Jeong and Ji han were drunk 😭
In another universe, isoo has a great relationship with his father, they occasionally drink together and his father reminisces about her mother and tells isoo how they fell in love and they both are happy and alive🥹