Conversation so far:
What was Helloween for Michael Kiske?
Helloween is a German power metal band.
When did Michael Kiske join the band Helloween?
At the age of eighteen
What did Michael Kiske do in the band Helloween?
He joined Helloween in late 1986.
Are there any other interesting aspects about the Michael Kiske article after joining Helloween?
Both Pink Bubbles Go Ape and Chameleon were commercial failures and resulted in Kiske leaving Helloween.

Question: When did he leave?
Self-contained rewrite: When did Michael Kiske leave the band Helloween?