My brother transferred our Mumbai flat to his name without my consent?

I discovered last week that my brother transferred our shared flat in Mumbai solely to his name. We inherited it from our parents. I never signed any documents, but he somehow managed to get it done. I'm feeling completely betrayed and don't know what steps to take. This flat is worth around ₹1.5 crores and I don't want to lose my rightful share. What legal actions can I pursue to challenge this transfer and reclaim my rights?