His bandmates broke the news to tearful fans during a live taping of TRL on Monday (July 9). The band will postpone the rest of its Black and Blue tour while AJ, 23, gets well.

Everything seemed fine last week, when the boys performed live on NBC's Today Show, as you can see for yourself in our photo gallery. But according to his publicist, McLean was battling depression brought on by the death of his grandmother, with whom he was very close.

"AJ is our friend and our brother and we whole-heartedly support him during this difficult time," the band said in a joint statement. "Fortunately, AJ has realized he can't solve his problems by himself.

"Because he is unable to be on tour at this time, we are postponing dates and will make them up as soon as we can," the group added. "At the same time we trust that our fans -- who've always stood by us -- will understand this decision is absolutely necessary in order for AJ to be well. We look forward to seeing all of you on the road soon."

Rescheduled dates will run from Aug. 7 in Vancouver, British Columbia to Sept. 28 in Edmonton, Ontario.