My cat is 12 and I have had him since a kitten. We recently moved into a new home with my fiancé and her 18 year old daughter 2 months ago. Loki seemed to be adjusting well, but just last week, he witnessed a loud bang when the daughter tripped towards him and he went into attack mode and chased her back towards her bed with the claws out. Since then he hisses at her and even stalks her when she is present. His aggression even differs to others if you get in the way. How can I get this behavior to stop as she is afraid of him. He is extremely friendly to everyone else and has never acted like this before.