New partner baby mum drama

So ive been with my new partner shy of 3 months we have kept things quiet up until now last night he had a call from his baby mum who he has no contact with unless its do with his children so he answered and she started kicking off about me saying im this and that she does not know me and i would never stop or prevent him seeing his children and would respect that she does not want me around them just yet but when she started i stayed quiet as hard as that was as i knew it would cause dramas for him seeing his kids what would you do as i cant stay quiet for long and let her think its ok to talk to or bout someone like that she sounds like a complete psychopath funny thing is she is in a relationship herself so i cant see the problem