That it was his "fiancee" that he hit? If so, proven, her name is listed in the police report that is available for public viewing.
If the question is whether he has another baby mama, also proven or at least admitted by Jones himself. Apparently this daughter is the oldest of all his kids and with a different woman -
"Jones has mentioned a fourth daughter in a couple of interviews, but has not opened up much about her. However, he often shares his family pictures on Instagram."
Jon Jones' daughters: A look at the UFC great's family (sportskeeda.com)