The 24-year-old is the second big-name departure from the Emirates this summer after Robin van Persie’s transfer to Manchester United.
“I am very happy for being here in Barcelona,” said Song. “It is a great day for me and my family.
“A few weeks ago I was waiting for the confirmation of an extension of my contract with Arsenal. And then Barcelona came along and I did all I could to get that because it is a once-in-a-lifetime opportunity to be able to play in a club like Barça.
“The best club in the world. I also want to thank Arsenal, Arsène Wenger. They have allowed me to be here.
“I knew that Barça is a team that has won everything. But I also know that is a team that is prepared to keep winning everything. And because of that I am very happy for having arrived here.
“I am convinced that we can win everything. I really want that and I am in the perfect team to achieve that.”
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