The stars of JYP Entertainment delivered an explosive first collaboration concert on December 24th. Fans naturally expected Park Jin Young, the Wonder Girls, J-Lim, 2PM, miss A, JOO, and San-E, but they were left gasping for air when former JYPE artists Rain, Son Ho Young, and Kim Tae Woo all made their cameo appearances throughout the concert. From blurry group photos to cute selcas (before and after the show), fans were given a sneak peek into what went down backstage. Already hyped for their concert, the atmosphere backstage sparked into a wildfire of congratulations and well-wishes, as San-E celebrated his 100th day since his debut. One JYP Nation member even took an interesting photo with him, but concealed his identity by wearing a mask. Can you guess who it is? Check out the photos below! [gallery]