Know vs knew, are these forms ungrammatical? [closed]

Solution 1:

According to me, knew and know have been used in a fairly appropriate sense here. However, I think that the grammatical issues here arise not because of the use of knew/know, but rather the framing of the rest of the sentence. It probably should've been framed as: " I knew that Willis was an idiotic oldie for years, but I didn't know he was such a retard. "

Solution 2:

The only ungrammatical thing I notice is that the "didn't" should have an apostrophe as shown here. Or you could use "did not" instead. Otherwise grammatically fine.

Does that answer your question?