T.I.'s collaboration with Christina Aguilera

Producer Alex Da Kid, who has worked on B.o.B and Hayley Williams' Airplanes and Eminem and Rihanna's Love the Way You Lie, recently revealed that he has another star-studded collaboration in the mix between T.I. and Christina Aguilera called Castle Walls, which will be featured on the rapper's new album, No Mercy!
He reveals:

"It's going to be T.I.'s next single. I love it. I think it's amazing. It's my sound, just kind of an evolution of that. I think it'll cater to a lot of different people."

Christina had this to say:

 “Yeah, he’s now incarcerated in jail… but (laughs) sorry not to laugh about people being in jail.  I did a song with Alex The Kid, the producer, called ‘Castle Walls’ and it’s probably going to be released as one of the singles off his upcoming album.”