The correct answer is Option 2)i.e. I have another. Key Points In the given sentence, the subject ‘I’ have already introduced my brother ‘Oliver’ and now we are talking about a different brother. The use of ‘other’ is incorrect before ‘brother.’❌ The most appropriate determiner for the given sentence is ‘another’.✔️ When we use the indefinite article ‘an’ before other, we write it as one word another. ‘Another’ means ‘one more, an additional, extra, an alternative or different’. Example: Is there another café around here we could go to? (alternative or different) We use another with singular nouns. Here, in the given sentence ‘brother’ is a singular noun. Therefore, by reading the above explanation we find that option 2 is correct. ?Correct sentence: You’ve met Oliver, but I have another brother whom you haven’t met, called Lucas.✔️ Additional Information Another is singular. We don’t use it with plural nouns. Example: Another interesting places to visit include the old harbor and the castle.❌(Incorrect) Example: Other interesting places to visit include the old harbor and the castle.✔️(Correct) We write another as one word. Example: There is an other car park a little further down the same street.❌ (Incorrect) Example: There is another car park a little further down the same street.✔️ (Correct) The words another and other mean the same thing, except that another is used with a singular noun and other is used with uncountable and plural nouns.