“Hey man, are you good?” AJ McLean had reason to be concerned about Liam Payne. Since production wrapped on the new Netflix music competition series where they’d met earlier this year, the Backstreet Boys veteran and One Direction star had talked almost every day on WhatsApp — at least until Payne’s sudden two-week silence early last month. Plus, McLean, 46, knew Payne, 31, had struggled with addiction.

On the set of “Building the Band,” where Payne was a celebrity mentor to contestants and McLean the host — the two forged an unusually tight bond over their shared experience: starting their careers in the crucible of teen celebrity and later battling substance abuse. “He was an absolute light, such an old soul,” McLean told The Times this week, describing the “very older brother” feeling he developed for Payne. “But you could tell you were talking to someone who had seen some s—, who had not lived a normal life.

” McLean, who had his three-year sober anniversary in September, said he did not believe Payne was using drugs during the period when the Netflix program filmed. He said they often spoke “candidly about sobriety, sharing stories and one-upping each other. We could laugh about it all, because if you’re still there to talk about it, that means you’re moving in a good direction.

” As it turned out, though, Payne was again fighting his demons. On Oct. 16, one day after McLean texted his final check-in, the singer fell to his death from .