Brother registered our Delhi property in his name without informing me?

I just found out that my brother registered our shared ancestral property in Delhi entirely in his name without my consent. This property was supposed to be shared equally among us, as per our late father's will. I feel completely betrayed and worried about losing my rightful share. What legal action can I take to reclaim my portion? Is there a way to challenge this unauthorized registration? I'm feeling so lost and desperate. Please help.