Jaejoong mentioned Maximilian Hecker** [LINK] in his Q&A with Kpop Planet:
5 (Ann, United Kingdom) : If you were given a chance to collaborate with international artists, who would it be and why?
Wow, I would love to collaborate with L’Arc-en-Ciel and Maximilian Hecker!
Maximilian Hecker posted Jaejoong’s message to him in one of his video (@ 3 min 2 sec):
** Maximilian Hecker is a German musician (wiki)