Lessee cannot deny the title of the landlord

Dear PAO,

I own a piece of land in Pasig City, where I built two houses. In 2018, one of the two houses was rented to Julia on a monthly basis. A contract of lease was signed covering the transaction. She was religiously paying her obligations for two years until she missed them. The total unpaid rent has been running for six months. In one of our conversations, she claimed that she would not pay the rent because she found out that I was not the real owner of the property. Is Julia justified in refusing to pay the rent based on her claim that I do not own the property?