Song is on loan at West Ham from Barcelona, and the fourth-placed Hammers travel to Stamford Bridge hoping to take points off the Premier League leaders.
The 27-year-old, who played 143 league matches for Arsenal, said his former team-mate from the Emirates Stadium and at Barcelona was a close friend - but that took nothing away from his desire to consolidate West Ham's top-four standing.
"Cesc is my brother from another mother. A good guy and a good player," Song said, as reported by The Mirror.
"I've known him since I was 17 when I signed for Arsenal. We grew up together. Then I moved to Barcelona.
"On the first day that I arrived at Arsenal I slept at his house. I was supposed to go to a hotel, but he said 'no'. He told me to stay with him at his house. He gave me advice to help me get started and it is always a pleasure to see him.
"I'm so happy with the way Chelsea are playing with him in the team. It's great because in his last year at Barca he didn't get to play in every game.
"It's very difficult when you are not playing at Barca as you have a lot of big ¬champions and everyone wants to play.
"So he was unlucky not to start every game, but he has shown his quality at Chelsea and he has reminded people that he is still a top player.
"I'm very happy for him, but I look forward to seeing him on the pitch so that I can win against him - then after the game we can be brothers again."
Song's West Ham then host Arsenal on Sunday two days later, in an emotional 72 hours for the Cameroon international.
"I was talking with my wife the other day and I said to her: 'These are two good games, but games where I will see some very important people to me'," he said.
"It will be difficult because my job will be to win those matches and I will fight hard to do that. But it will mean a lot to see them [Fabregas and former coach Arsene Wenger] again."
