Signed from Benfica barely a day ago, Carreras was presented to the local press this morning at the Santiago Bernabeu.
The wing-back, formerly a Real youth teamer before he left Manchester United, Carreras says being back at his formative club is a dream come true.
He said: "It means everything. Fulfill a dream and return home where I have incredible experiences. I have many to face this challenge. It's a dream.
"The road has been long. There is a lot of talk in football. I was focused on Benfica. It didn't go as we expected in the World Cup. I'm looking forward to starting a season that's going to be brilliant for everyone."
On Real coach Xabi Alonso, he also said: "I have had the opportunity to speak with him. He offered me luck and the position in which I was needed."
Carreras also said: "It's the happiest day of my entire life. I'm ready.
"It's hard to describe yourself. I am a player who likes to have the ball. I like to move forward and above all defend well. But above all, give my best with this shirt.
"I am inspired by Roberto (Carlos) and Marcelo. They were my inspiration. I was able to see Marcelo live and it was a luxury. They are my references."