I have 6 month Doberman mix who is the sweetest puppy in the world. Whenever we go on walks, he is extremely friendly to every dog and anyone who asks me if they can pet him. We have had 0 aggression issues apart from 1 incident.

Me and my family had taken him for a vacation where sadly he got attacked by two off leash dogs (one a pet, and the other a stray). He hurt himself jumping into the car but apart from that, the dogs were not able to physically touch him. That same weekend, we invited this cousin and their family with their dog to our place. Now my cousin's puppy is also the same age and like mine, well socialised and incredibly good with people and other dogs. But as soon as the puppy entered our house, its like a switch turned on for mine. His hair stood up, and he started 'grrrrring' and tried to attack my cousin's puppy. We had to keep them separated the entire evening, for about 2-3 hours and my puppy was 'grrring' at him the whole time. Like, I am obviously no expert but I was worried he would cause some serious damage if he could have, maybe even kill him.

Fast forward a few weeks, there is a dog meet in my city, arranged by our trainer and everyone is free to attend. I have been wondering, should I tell my cousin to attend with her dog? Will mine remember and try to attack like last time? Or was he just being extremely territorial because they met for the first time in our house (a mistake I dont intend to make once again)? He has never shown this kind of territorial aggression towards the many dogs of neighbours who have come inside our house a few times. What things should I consider before making a decision? Will my puppy even remember that incident? I want my puppy to spend time socialising and playing with the dogs that will be there at the puppy meet and not fighting with another puppy and being on leash the whole time.