London, Jan 16 (Agencies): Backstreet Boys member AJ Mclean has returned to rehab for the third time citing personal reasons.

The 'Millenium' singer has been battling substance abuse for years, enrolling in rehab in 2001 and 2002, reported Sun online.

The 33-year-old singer tweeted, "I love u all and wish me luck! I start my sober journey tomm (sic)!"

A source said that AJ, who struggled with sobriety in recent months, is now out of control.

The band is due to hit the road for their upcoming co-headline tour with 'New Kids On The Block'.

The Backstreet Boys have sold over 130 million records worldwide, making them one of the biggest selling artists of all time.