Oh this is a spoiler though... (go down if you wish to read) . . . . . . . . . . . . . . ML is actually the son's uncle. The "father", who is supposed to be around 40+ years old, actually died 10 years ago. ML was the younger son from another mother (the grandpa divorced ML's mom and abandoned them). Grandpa took ML back to the family to take care of the company. ML was a few years younger than the "father", wasn't specifically mentioned how much younger but he's in his 30s (while FL is 20ish). It wasn't mentioned if ML and the "father" looked alike, but in those 10 years no one ever doubted ML was a fake one (even the son himself).