Producer of “Airplanes” and “Love The Way You Lie” fame, Alex Da Kid, is dipping his hand in the formula once again. The worlds of Hip-Hop & Pop meet again for Kid as T.I. and Christina Aguilera collaborate for “Castle Walls.” The song is the official second single from T.I.’s No Mercy.

The song is the same affair of a female on the hook but there’s an added bit of electro that we haven’t heard before in an Alex Da Kid production. Aguilera’s subtle approach on the hook makes her the highlight of the song but as to whether or not this song blows up is another situation. Rihanna’s vocals still, to this moment, sound off on “L.T.W.Y.L.” but it was #1 because of the star power behind the single. This really is not the case with T.I. and Aguilera, right now. Take a listen below to the new single.