My oldest Nuggie is also very protective of his garden and no cat was safe....this has included my 2yr old & 7mths old. This also extends to him not even letting them re-enter the house
It hasnt gotten as violent as your situation though
and Nuggie is generally all mouth. He is more accepting of Evie (7mths) as she is such a whirlwind, appears from no where and generally makes his garden patrol much more difficult, so accepts her rather than tries to keep up with her lol
But in the house they are all friends and sleep near each other
Cats are funny. They do not recognise others by sight alone, but by scent. Do they normally meet/share the house?? It could be he did not recognise her, saw her a threat (especially protecting kittens) and its ended so very badly
I agree with the Feliway and all advise here - it might be worth to start all over again with introductions?
Often cats never become good friends, but can still live together relatively incident free, so it could definitely be worth retrying intorductions.
Poor Jess, bless her