When Casals laid eyes on cello music he never knew existed....
I thought the verb 'existed' belongs to the antecedent, 'cello music', and 'he never knew' is just an embedded clause in the sentence. So the sentence could be 'When Casal laid eyes on cello music which/that he never knew existed...'. Is that correct?
Here, I need an explanation. I've learned relative pronouns as subject cannot be omitted. If it is right, how is it possible to omit 'which' or 'that' in that sentence? Shouldn't I put 'which' or 'that' in the sentence? If the relative pronoun 'which' cannot be put between 'cello music' and 'he never knew existed', the clause 'he never knew existed' has two main verbs, which looks like a pretty weird sentence to me...
Please help me figure out how this sentence works. Thanks.