I'm trying to remember when the boys found out the truth about Heaven. When they learned that Zach, et al, had been the ones behind everything and that they *wanted* Lucifer to rise.
Was it season four or five? An exact episode isn't necessary, but 'late in season four' or 'first couple eps of season five' would be fine.
ETA: Already answered! Whooooooosh! You guys are fast. :)