Learn German: Die Band, deren Album wir morgen veröffentlichen, ist toll. - The band whose album we are publishing tomorrow is great.

The word deren (whose) refers back to die Band. Because Band is a feminine noun, we use the feminine genitive relative pronoun deren. If we were talking about a masculine or neuter noun, we would use dessen.

Does deren change its ending depending on the word Album?

No! Unlike normal possessive adjectives (like mein or ihr), the relative pronouns deren and dessen never change their endings to match the noun that follows them. They only depend on the gender and number of the noun they refer back to (in this case, the feminine noun die Band).

What case is the phrase deren Album in the relative clause?

The phrase acts as the direct object of the verb veröffentlichen (to publish), so it is in the accusative case. Even though the word Album is accusative here, the word deren stays locked in the genitive case because its only job is to show possession (whose album).

Why does the verb veröffentlichen come right before the second comma?

The section between the commas is a relative clause. Relative clauses act like subordinate clauses, meaning the conjugated verb (veröffentlichen) must be pushed to the very end of that specific clause.