Gundogan left Barca for a return to City in the final days of the summer market.
He recalled to the Daily Mail: "When I was sure it would be amazing to come back, I spoke with Pep (Guardiola, manager).
"I called him and asked him if he could imagine it. Not out of nothing. I had thought about it. it was something I personally wanted to do and I didn’t have much to lose, you know?
"I was a bit nervous beforehand but it was a nice call. Obviously my relationship with Pep was always good. Even though I was in Barcelona last year we had a few phone calls between each other. We actually also met there once.
"There is no reason to hide that we have a good connection but at the end you never know how people will react or what they think about certain situations.
"So when I mentioned it and I got a great response, I was relieved. It was something that maybe I didn’t quite expect in that moment. He said had it been up to him it would have been done tomorrow."
On his year with the Blaugrana, Gundogan also said: "You know, I think I had a successful time over there.
"I mean apart from anything, I played for one of the biggest teams in the world. I fulfilled one of my childhood dreams, playing for Barca and wearing that badge.
"Maybe people will look at last season and think we didn’t win anything. That’s true. But if you look at how we performed we had 85 points at the end of the season, only three less than the previous year when they won the league.
"We were playing against a really difficult Real Madrid side. I feel very privileged to have played for Barcelona. In other circumstances maybe things would have turned out differently.
"It was a tough but also great experience. So no regrets at all."