My brother sold our apartment in Mumbai without telling me, what are my options?

I'm shocked and hurt. My brother sold our jointly owned apartment in Mumbai without my consent. We inherited it from our parents. I only found out when the new owner contacted me. I live in Delhi and was not involved in any part of the sale. I'm worried I'll lose my share. What legal action can I take to secure my rights? Is there a way to reverse this sale? Please help, I'm feeling so betrayed.