The pairing started in the beginning of 2011 when both groups were promoting at the same time. It was when DBSK made their comeback as a duo with their debut song KYHD and Secret came with their fourth single Shy Boy. But their official appearance together was on Changmin's Birthday when they were backstage together at Music Bank and that day was when Secret won their third award (in MB). Before their appearance together, they had interviews praising each other, Secret doing the KYHD move in their choreo and so on. Then, on the K-Pop Festival in Bangkok, there were some Yunho/Jieun moments in the press conference as well on the ending. After that, nothing really happened and now in 2013, Yunho and Hyosung had a brief eye contact on a fancam that I saw. But what really took the toll on the shipping was Changmin and Sunhwa's moment on Moonlight Prince.

Now, some media:

Secret + DBSK Interview

Credits to MegaKPOPVideos

Secret's reaction when DBSK won. I must say, that would had been the perfect moment for them!

Credits to aiai qiqi

Their first appearance together with a shy Changmin~

Credits to kpoplivehd3

Secret's win on the same episode. DBSK cheered for them in the back

Credits to vietanhmsg1

Another win by Secret and DBSK cheering for them once again

Credits to jason kay

Secret doing the KYHD dance in their choreography

Credits to kbsworld

Secret as MC's and praising DBSK

Credits to secretbr2011