gackt and hyde

[ayuayu]

hi i recently rediscovered my gackt CD's and got into him again and while i was on the internet looking for the lyrics to "cube" i saw that at least one of his songs was done by hyde. i've heard the song "horizon" by hyde and they sound a little similar, i also saw on yesasia a calendar of them together and they were in a movie. what is the story with these two? are they good friends?