The 23-year-old Turkey international becomes new Reds boss Brendan Rodgers' fourth new arrival following Joe Allen, Fabio Borini and Oussama Assaidi. The Merseysiders saw off competition from Arsenal for Sahin, who helped Madrid win the Primera Division title last season, and the player said former Reds midfielder Alonso's passion for the club convinced him it was the right move.
Asked whether he spoke with Alonso before making his mind up, he said on www.liverpoolfc.tv: "Yes, of course. A lot of times. Xabi is a person who really cares about football. He's in love with football. I'm the same, and that's why we had a lot of conversations."
He added: "When I arrived at Real Madrid, we spoke about German football and Italian football. He likes football! When he heard Liverpool were interested in me, he started telling me about Liverpool.
"He is still in love with Liverpool Football Club, I think. It's crazy how he was telling me about Liverpool. He was saying, 'Go there - you will love it. The fans will take care of you and love you' and things like that.
"He said Anfield is the best stadium in the world. Xabi won a lot of trophies here, and hopefully we can do that too."