Co-founder trying to patent our startup's product without my consent?

I co-founded a tech startup in Bengaluru with a friend. We've been developing a unique software product together. Recently, I discovered that he filed a patent application for our product, listing himself as the sole inventor. This was done without my consent or even informing me. I feel betrayed as I invested not just money but significant effort in the development. What legal steps can I take to contest this patent application and protect my rights and contributions?