Tenses and conditionals

[Raymott]

and I can't get its grammatical justification.

Thanks,

Not everything comes down to grammatical justification.
We don't say, "I just met a woman I've never heard of before. I didn't know she was so tall."
We do say, "I just saw Rhonda, who I've been emailing on the 'net. I didn't know she was so tall."
I have no further explanations except to say that the first is silly because there's no reason you should have formed an opinion about something you've never heard of, like a movie or an unknown person.