The winger made the move after just one season of senior football with Mainz.
He recalled to the club's website: "The club had been watching me for some time and obviously the coach knew about me from playing in the Bundesliga last season with Mainz. When I first met the coach, he told me he was impressed with what I could do on the pitch as a creative player, a technical player, and hopefully the fans can now see that as well.
"It was a tough situation for me. I had only just turned 20 and I had just got used to playing first-team football. Now I would be leaving my home, my family, my friends and the coaches and teammates who had helped me to this point. But when Brighton told me that they wanted me, how could I say no?
"The Premier League is the best league in the world and when I came over and saw what we have here: the training ground, the facilities, the changing areas, the kitchens, everything was so professional. Straight away I felt comfortable here and I knew this was the right choice for me. My family also arrived recently to visit me, so it’s been good to have them here with me."