Song is looking forward to be re-united with former Arsenal team-mate Cesc Fabregas at the Nou Camp.
He told Barca TV: “Today is a very good day for me and my family. Very happy to be here, this is the best team in the world, playing at a club like Barça is something I wanted when I was young.
“I hope the team will continue to win, this is a winning team. They win everything. I will give my best on training and when I get the chance to play I will do it.”
“I know Cesc very well, I slept at his house last night,” he added. “He’s a very good friend of mine, he will help me to integrate.”
