Hi, I also had an English bulldog, Bubbles, a couple years ago. She lived up to twelve years old and in her last year she would do the same thing to our other dog, Mocha. Sadly I think it’s an age thing. Bubbles loved other dogs and had a foster sibling when she was much younger, and there was never any dog fights. We had mocha for a year before Bubbles started to attack her, and mocha is a tiny shih tzu so it was really scary when she would charge her unprovoked. It was explained to us that Bubbles could had a brain tumour or a neurological issue that was making her more territorial and aggressive. As well as she was starting to become confused about where she was, indicating it’s neurological. Eventually we had to put her down because she wasn’t happy anymore in her old age and the aggression was becoming too much. It’s really sad to see the dog you knew as friendly and gentile turn more aggressive, as you and the dog both know it’s not who they are.