Brother took joint property loan in Delhi without informing me, what can I do?

I just found out that my brother took a loan of ₹15 lakh against our jointly owned property in Delhi without my knowledge. The bank is now demanding repayment notices to both of us. I am really upset as this affects my financial standing and I had no idea about this arrangement. I trusted him completely and now I feel betrayed. What are my legal options to handle this situation? Can I contest the bank’s demand? What about the loan validity?