who has legal right to ownership of home

When your ex paid off the home, i imagine that he was with you at the time and loved you and was paying the loan out of his own generocity, without the expectation that he would have an ownership interest.  However, he probably figured that he was going to be marrying you and that the house would be marital property.  Nevertheless, his paying off the loan does not give him ANY ownership interest whatsoever.  Therefore, he is not entitled to claim an interest. Plus, to have an interest in real estate there must be a contract in writing.  No such thing exists here.  Therefoe, you should not have to worry about him claiming an interest and prevailing.