BSB may have added an NKOTB -- but will they now lose a McLean?

On Thursday, Backstreet Boy A.J. McLean announced to fans that he'll be seeking treatment ... for the third time. The 33-year-old singer, who has a history of substance abuse problems, said he wants to get cleaned up before his group's tour with New Kids on the Block begins.

"For personal reasons, I've checked myself into a rehab clinic," McLean explained in a statement. "With 2011 being a busy year for Backstreet, I want to be healthy and perform and sing for people at my very best and happiest. None of this will affect our current tour plans and I look forward to seeing everyone really soon! Thank you for all of your support and respecting my family and friends privacy during this time."

Over the weekend, A.J. hinted via Twitter (of course) that a rehab stay was coming. "Thank u all for my bday wishes and tweets:)! Its gonna be a great year! I love u all and wish me luck! I start my sober journey tomm! Ttfn!" he wrote.

NKOTBSB will kick off its summer tour on June 2.

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