It was already revealed that he collaborated with Aerosmith's Steven Tyler and people are strongly suspecting that he also worked with Snoop Dogg. It appears this album will feature a lot of famous singers, perhaps both in and outside of South Korea.
It appears January is going to be very competitive with many comebacks, considering Rain, TVXQ, and Girl's Day will be releasing albums next month. In addition, Girls' Generation and Rainbow were rumored to likewise be returning in January!
Stay tuned for updates on all of these pending comebacks!