"The reasons I left Spurs are that I am a huge Liverpool fan and the chance to play for them may never come around again.
"This opportunity is something I couldn't let go. I am at an age now when I believe I am at my peak, and aim to kick on."
Keane's move has been criticised by Spurs chairman Daniel Levy, but he does not believe he betrayed the White Hart Lane outfit down by leaving.
"I do not think I let Spurs down. I had six fantastic seasons there and gave them everything, from day one," he said.
"I always give everything, and that will never change. The Spurs fans were always magnificent to me and I will always have a place in my heart for them.
"But this is a new chapter in my life and one that I am looking forward to. I had six great years at Spurs and thank them for that."
Keane, who is the Republic of Ireland's record goalscorer, says he cannot wait to begin his partnership with the club's Spanish sensation Fernando Torres, who scored 33 goals in all competitions in his debut season last term.
"He has been a revelation since he came to the Premier League," said Keane. "He was absolutely outstanding last year and also in the Euros with Spain.
"It is hard to leave Tottenham with some of the players they had - like Dimitar Berbatov, who I had a great relationship with - but Torres is probably the best striker in the world right now.
Keane is a lifelong Liverpool fan
"Hopefully we can play a lot of games together and do well."
Keane also revealed his pride in being handed the number seven shirt at Anfield, following in the footsteps of the likes of Liverpool legends Kenny Dalglish and Kevin Keegan.
"To wear that shirt is an honour, and something I truly understand. If I can have half as much success in it as Keegan and Dalglish did, I will be a happy man," he said.
Reds boss Rafael Benitez says he hopes the shirt inspires Keane to succeed at Liverpool.
"We were talking about the number, and the big names that have had this number, so it will be inspirational for him to have it too," said the Spaniard.
"We were looking for a player with game intelligence and good movement who could play alongside Torres.
"He can play with Torres up front and also on the right. He is a player who can give to us a lot of goals - normally he gets about 15 each year.
"We were looking for the workrate he can give to us, the game intelligence and also the goals."
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