Antonio Rudiger said on Monday Carlo Ancelotti was instrumental in his decision to join Real Madrid from Chelsea this summer.
Rudiger has moved to the Santiago Bernabeu on a free transfer after choosing not to extend his Chelsea contract. The 29-year-old defender has signed a four-year deal with the reigning Spanish and European champions.
Rudiger, speaking at his presentation ceremony at the club's training ground in Valdebebas, said he made his decision in April, after a conversation with the Italian coach.
"The first time I got in contact, not really me, my agent, was early September. The second time, I spoke with Mr Ancelotti, that was in April," Rudiger said.
"That was the most important moment, to speak with Mr Ancelotti. That was when I made my choice, that I wanted to play for this club under him.
"He said he wanted me, trusted in my abilities, that I could be very helpful to the team, and at my age, that's enough. At the end of the day, it's Mr Ancelotti. You always know at Madrid that nothing is guaranteed. You have to fight for your place. I'm ready to do that."
As well as turning down the chance to stay at Chelsea, Rudiger said there was also interest in him from Barcelona. "There was interest from Barcelona but I told my brother, it's Real or nothing," Rudiger said.
The German will be competing with Eder Militao and David Alaba for a spot in Madrid's central defence next season, although Ancelotti could also switch to a back three in defence to accommodate an impressive trio of options.
After the departures of Sergio Ramos and Raphael Varane last year, Militao and Alaba formed a superb partnership, becoming an essential part of Madrid's success last term.
"Real Madrid is stacked with very, very good players, also in my position," said Rudiger.
"But I'm looking confidently going into this. What do I bring? Competition, which is healthy for everyone. It keeps everyone going and I'm looking forward to the challenge."
Rudiger became known at Chelsea for his combative style and dynamic displays in the Premier League. He pledged to be a leader in the Real Madrid dressing room.
"With me you never know what to expect off the pitch. I like to laugh, I like to dance," said Rudiger.
"But on the pitch I'm serious. I don't like to joke around. I hope what I can bring is my fighting spirit, leadership. Rome wasn't built in a day. I have to come here, adapt, speak Spanish. I will do my best."
Asked if there were any Real Madrid defenders he particularly admired, Rudiger said: "There have been a lot of top centre-backs but one I liked a lot was Pepe. Apparently off the pitch a very nice person, but on the pitch, a monster. I like that," Rudiger said.
Rudiger was on the pitch, and scored, as Chelsea led 3-0 at the Santiago Bernabeu in April, only for Real Madrid to pull off an incredible comeback to reach the Champions League semi-finals.
"It was a very intense night, it was my first time at the Bernabeu," Rudiger said. "What Madrid did last year in the Champions League, that was... I don't know how to describe it, unbelievable."
Madrid defeated Liverpool 1-0 in the final in Paris, to lift the club's 14th European Cup.
"In the final, I knew I was going to be a Real Madrid player and I was rooting for them," Rudiger added. "I lost two finals against Liverpool with my former team so I was very happy that Real beat them."