My brother forged my signature to sell our parents' house in Pune?

I'm from Pune and I just found out that my brother sold our parents' house by forging my signature. I had no idea about this until a friend mentioned seeing a 'sold' sign outside the property, and I confronted him. He admitted to it but refuses to talk further. I am worried and feel betrayed. The sale was finalized last week. What legal steps can I take to challenge this fraudulent sale and safeguard my share? Please advise, as I don't know how to proceed.