Aaron Carter once called AJ Mclean for help with addiction

AJ Mclean remembered playing a pivotal role in getting Aaron Carter back into therapy.

In the upcoming documentary Aaron Carter: The Little Prince of Pop, the Backstreet Boys member revealed his efforts to bring the late singer into rehab after he asked him for his help.

"2017, Aaron reached out to me, asked me for help. I said, 'Look, if you get on a plane, come out to L.A., I will make sure you get into treatment.' And he showed up," Mclean added, "I was shocked, but I was happy, and he checked into a treatment center in Malibu."

He said, "A couple days later, I talked to him, and then he kind of went off the map. I think it was maybe two weeks, so I called my friends at the treatment center, and they said he checked himself out."

The documentary will be available on Hulu on May 1. Powered by ABC News Studios, it depicts the Crush on You singer story as he dominated the pop industry in the early 2000s and his mental health struggles.