Donation between partners in a common law relationship is void

Dear PAO,

My only sibling purchased a house and lot after the death of our parents, and the property was registered in her name. She later met Jose, and they eventually lived together in the house and lot. Sadly, my sister died. Jose now wants to lease the property to a foreigner, but I protested because he is not the owner thereof. However, he claimed that my sister donated the house and lot to him when they were cohabiting. Who has a better right over the house and lot?