Peter - Sensei as soon as I mentioned you to Kostas - Sensei, he made the thumbs up.
He said that he was waiting for you come this summer and he will of course be waiting for you next summer.
He also sends his regards.
Kostas - Sensei also seems to be a very good person and not only a very good teacher. I hope I will learn a lot from him. You are also welcome to come anytime.