I am so thankful for this forum! My 2 adult boy cats have been together for over 10 years with absolutely no problems. Recently (within the last 2 weeks) they have begun fighting violently! This is not play-fighting! They have been "soul mates" all this time and now I'm afraid to leave them alone as one is twice as big as the other one and I don't want to see either one injured. There has been no change to their environment, food, or other patterns in their lives so I am at a loss over this. Realizing it is the season for many female cats to go into heat, I considered whether there may be a female in the area. I do know my neighborhood has many feral cats which I can do nothing about because everyone feeds them, so I am concerned about the ferals introducing diseases, fleas, etc., that may have affected my boys. When they fight, I separate them for a time, then slowly "reintroduce" them to each other; even coaxing them with a little "nip" so they'll "make nice"! They go back to their normal behavior for a couple of days then boom, they're fighting again. The behavior is getting more frequent. If anyone has gone thru this, I'd really appreciate what you experienced and what, if any, remedy you used. My last resort will be to take them to the vet but would like to understand the behavior first. Any suggestions will be greatly appreciated! Thank you!