They talk about Changmin At 03:52~ 04:30:

[Trans]

QNS: who do you think it will be if you add another member to D&E?
MC: siwon-ssi??
Donghae: shhhh
Hyunk: shhhh
Donghae: siwon? Nono… he doesnt fit with us
Hyuk: firstly, he has to match our heights. Siwon is too tall…so he cant.
MC: ah.. who would it be then?
Donghae: max changmin?
Hyuk: ah TVXQ’s changmin… even though he is not our member but for changmin. he is a friend that really loves D&E. Like our choki wa’s stage, he wanted to do it with us during TVXQ’s concert a while back so he invited us as guests and we did it with him. He also personally came to watch our D&E’s japan concert too so it was very enjoyable

——————-

Credits:

Video by Yik Ming Wu
Translated by @teukables
Shared by TVXQ! Express