2 of my 5 cats no longer getting along

[lljones5523]

I can relate! My male cat, 10 years old, has begun attacking my youngest cat (five years old). I had four cats and just recently put down the oldest, she was 22 years old. Since then, he has begun attacking her to the point of real aggression. She gets trapped in the bathrooms, he corners her then attacks.
If I am home when this happens I spray him with a water gun however the behavior hasn't stopped.
Any input would be greatly appreciated!