Wirtz joined the Reds for a club record £125m.
He said in a recent documentary: "I'm really happy about this (that I left Leverkusen on good terms).
"I would be really sad if it was the opposite.
"We achieved really, really big and incredible things together. In the end, we talked and were trustful and straight to each other to make the best possible thing for the move.
"Everyone was happy in the end and that's what really matters for me and I'm really happy about this."
Meanwhile, Wirtz's former youth coach at FC Koln, Markus Daun recalled: "I asked him in a meeting about his career goals," Daun recalled. "All the guys from the team said, 'Oh, I will be German championship winner this year and I will be in the starting XI.'.
"Florian said: 'I will win the Ballon d'Or in the future.' And I said, 'okay'.
"Normally I would say, 'Okay, please stay realistic,' but in this case I said, 'Okay, go your way and you can achieve it!'.
"I knew from the beginning that he will go his way until the top of the world."